write_file() either returns 0 or dies, so there is no point in checking
its return value.  The callers of the wrappers write_state_text(),
write_state_count() and write_state_bool() consequently already ignore
their return values.  Stop pretending we care and make them void.
Signed-off-by: NRene Scharfe <l.s.r@web.de>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The 'v'iew subcommand of the interactive mode of "git am -i" was
broken by the rewrite to C we did at around 2.6.0 timeframe at
7ff26832 (builtin-am: implement -i/--interactive, 2015-08-04); we
used to spawn the pager via the shell, accepting things like

	PAGER='less -S'

in the environment, but the rewrite forgot and tried to directly
spawn a command whose name is the entire string.

The previous refactoring of the new helper function makes it easier
for us to do the right thing.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Now there is no direct caller to strbuf_getline(), we can demote it
to file-scope static that is private to strbuf.c and rename it to
strbuf_getdelim().  Rename strbuf_getline_crlf(), which is designed
to be the most "text friendly" variant, and allow it to take over
this simplest name, strbuf_getline(), so we can add more uses of it
without having to type _crlf over and over again in the coming
steps.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The strbuf_getline() interface allows a byte other than LF or NUL as
the line terminator, but this is only because I wrote these
codepaths anticipating that there might be a value other than NUL
and LF that could be useful when I introduced line_termination long
time ago.  No useful caller that uses other value has emerged.

By now, it is clear that the interface is overly broad without a
good reason.  Many codepaths have hardcoded preference to read
either LF terminated or NUL terminated records from their input, and
then call strbuf_getline() with LF or NUL as the third parameter.

This step introduces two thin wrappers around strbuf_getline(),
namely, strbuf_getline_lf() and strbuf_getline_nul(), and
mechanically rewrites these call sites to call either one of
them.  The changes contained in this patch are:

 * introduction of these two functions in strbuf.[ch]

 * mechanical conversion of all callers to strbuf_getline() with
   either '\n' or '\0' as the third parameter to instead call the
   respective thin wrapper.

After this step, output from "git grep 'strbuf_getline('" would
become a lot smaller.  An interim goal of this series is to make
this an empty set, so that we can have strbuf_getline_crlf() take
over the shorter name strbuf_getline().
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Often we read "text" files that are supplied by the end user
(e.g. commit log message that was edited with $GIT_EDITOR upon 'git
commit -e'), and in some environments lines in a text file are
terminated with CRLF.  Existing strbuf_getline() knows to read a
single line and then strip the terminating byte from the result, but
it is handy to have a version that is more tailored for a "text"
input that takes both '\n' and '\r\n' as line terminator (aka
<newline> in POSIX lingo) and returns the body of the line after
stripping <newline>.

Recently reimplemented "git am" uses such a function implemented
privately; move it to strbuf.[ch] and make it available for others.

Note that we do not blindly replace calls to strbuf_getline() that
uses LF as the line terminator with calls to strbuf_getline_crlf()
and this is very much deliberate.  Some callers may want to treat an
incoming line that ends with CR (and terminated with LF) to have a
payload that includes the final CR, and such a blind replacement
will result in misconversion when done without code audit.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Before auto-gc'ing, we need to make sure that the pack files are
released in case they need to be repacked and garbage-collected.
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

struct object is one of the major data structures dealing with object
IDs.  Convert it to use struct object_id instead of an unsigned char
array.  Convert get_object_hash to refer to the new member as well.
Signed-off-by: Nbrian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: NJeff King <peff@peff.net>

And finally the endgame.  Instead of spawning "git mailinfo" via the
run_command() API the same number of times as there are incoming
patches, make direct internal call to the libified mailinfo() from
"git am" to reduce the spawning overhead, which would matter on some
platforms.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NRalf Thielow <ralf.thielow@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This function is also used in other builtins than stripspace, so it
makes sense to have it in a more generic place.  Since it operates
on an strbuf and the function is declared in strbuf.h, move it to
strbuf.c and add the corresponding prefix to its name, just like
other API functions in the strbuf_* family.

Also switch all current users of stripspace() to the new function
name and keep a temporary wrapper inline function for any topic
branches still using stripspace().
Reviewed-by: NMatthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When "am" was rewritten in C, the codepath for falling back to
three-way merge was mistakenly made to make an internal call to
merge-recursive, disabling the error reporting code for certain
types of errors merge-recursive detects and reports by calling
die().

This is a quick-fix for correctness.  The ideal endgame would be to
replace run_command() in run_fallback_merge_recursive() with a
direct call after making sure that internal call to merge-recursive
does not die().
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The new builtin am ignores the user.signingkey variable: gpg is being
called with the committer details as the key ID, which may not be
correct. git_gpg_config is responsible for handling that variable and is
expected to be called on initialization by any modules that use gpg.
Signed-off-by: NRenee Margaret McConahy <nepella@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Linus noticed that the recently reimplemented "git am -s" defines
the trailer block too rigidly, resulting in an unnecessary blank
line between the existing sign-offs and his new sign-off.  An e-mail
submission sent to Linus in real life ends with mixture of sign-offs
and commentaries, e.g.

	title here

	message here
Signed-off-by: NOriginal Author <original@auth.or>
	[rv: tweaked frotz and nitfol]
Signed-off-by: NRe Viewer <rv@ew.er>
Signed-off-by: NOther Reviewer <other@rev.ewer>
	---
	patch here

Because the reimplementation reused append_signoff() helper that is
used by other codepaths, which is unaware that people intermix such
comments with their sign-offs in the trailer block, such a message
was judged to end with a non-trailer, resulting in an extra blank
line before adding a new sign-off.

The original scripted version of "git am" used a lot looser
definition, i.e. "if and only if there is no line that begins with
Signed-off-by:, add a blank line before adding a new sign-off".  For
the upcoming release, stop using the append_signoff() in "git am"
and reimplement the looser definition used by the scripted version
to use only in "git am" to fix this regression in "am" while
avoiding new regressions to other users of append_signoff().

In the longer term, we should look into loosening append_signoff()
so that other codepaths that add a new sign-off behave the same way
as "git am -s", but that is a task for post-release.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

There's a bug in builtin/am.c in which we take a lock on
MERGE_RR recursively. But rather than fix am.c, this patch
fixes the confusing interface from rerere.c that caused the
bug. Read on for the gory details.

The setup_rerere() function both reads the existing MERGE_RR
file, and takes MERGE_RR.lock. In the rerere() and
rerere_forget() functions, we end up in write_rr(), which
will then commit the lock file.

But for functions like rerere_clear() that do not write to
MERGE_RR, we expect the caller to have handled
setup_rerere(). That caller would then need to release the
lockfile, but it can't; the lock struct is local to
rerere.c.

For builtin/rerere.c, this is OK. We run a single rerere
operation and then exit immediately, which has the side
effect of rolling back the lockfile.

But in builtin/am.c, this is actively wrong. If we run "git
am -3 --skip", we call setup-rerere twice without releasing
the lock:

  1. The "--skip" causes us to call am_rerere_clear(), which
     calls setup_rerere(), but never drops the lock.

  2. We then proceed to the next patch.

  3. The "--3way" may cause us to call rerere() to handle
     conflicts in that patch, but we are already holding the
     lock. The lockfile code dies with:

     BUG: prepare_tempfile_object called for active object

We could fix this by having rerere_clear() call
rollback_lock_file(). But it feels a bit odd for it to roll
back a lockfile that it did not itself take. So let's
simplify the interface further, and handle setup_rerere in
the function itself, taking away the question from the
caller over whether they need to do so.

We can give rerere_gc() the same treatment, as well (even
though it doesn't have any callers besides builtin/rerere.c
at this point). Note that these functions don't take flags
from their callers to pass along to setup_rerere; that's OK,
because the flags would not be meaningful for what they are
doing.

Both of those functions need to hold the lock because even
though they do not write to MERGE_RR, they are still writing
and should be protected from a simultaneous "rerere" run.
But rerere_remaining(), "rerere diff", and "rerere status"
are all read-only operations. They want to setup_rerere(),
but do not care about taking the lock in the first place.
Since our update of MERGE_RR is the usual atomic rename done
by commit_lock_file, they can just do a lockless read. For
that, we teach setup_rerere a READONLY flag to avoid the
lock.

As a bonus, this pushes builtin/rerere.c's setup_rerere call
closer to the functions that use it. Which means that "git
rerere totally-bogus-command" will no longer silently
exit(0) in a repository without rerere enabled.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NJiang Xin <worldhello.net@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

All existing callers to this function use it to produce a text file
or an empty file, and a new callsite that mimick them must end their
payload with a LF.  If they forget to do so, the resulting file will
end with an incomplete line.

Teach write_file_v() to complete the incomplete line, if exists, so
that the callers do not have to.

With this, the caller-side fix in builtin/am.c becomes unnecessary.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

All callers except three passed 1 for the "fatal" parameter to ask
this function to die upon error, but to a casual reader of the code,
it was not all obvious what that 1 meant.  Instead, split the
function into two based on a common write_file_v() that takes the
flag, introduce write_file_gently() as a new way to attempt creating
a file without dying on error, and make three callers to call it.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

We forgot to terminate the payload given to write_file() with LF,
resulting in files that end with an incomplete line.  Teach the
wrappers builtin/am uses to make sure it adds LF at the end as
necessary.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

There are many calls to write_file() that repeat the same pattern in
the implementation of the builtin version of "am".  They all share
the same traits, i.e they

 - produce a text file with a single string in it;

 - have enough information to produce the entire contents of that
   file;

 - generate the pathname of the file by making a call to am_path(); and

 - they ask write_file() to die() upon failure.

The slight differences among the call sites throw them into roughly
three categories:

 - many write either "t" or "f" based on a boolean value to a file;

 - some write the integer value in decimal text;

 - some others write more general string, e.g. an object name in
   hex, an empty string (i.e. the presense of the file itself serves
   as a flag), etc.

Introduce three helpers, write_state_bool(), write_state_count() and
write_state_text(), to reduce direct calls to write_file().

This is a preparatory step for the next step to ensure that no
"state" file this command leaves in $GIT_DIR is with an incomplete
line at the end.
Suggested-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

After running "git am --abort", and then running "git reset --hard",
files that were not modified would still be re-checked out.

This is because clean_index() in builtin/am.c mistakenly called the
read_tree() function, which overwrites all entries in the index,
including the stat info.

"git am --skip" did not seem to have this issue because am_skip() called
am_run(), which called refresh_cache() to update the stat info. However,
there's still a performance penalty as the lack of stat info meant that
refresh_cache() would have to scan all files for changes.

Fix this by using unpack_trees() instead to merge the tree into the
index, so that the stat info from the index is kept.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Helped-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

After resolving a conflicting patch, a user may wish to sign off the
patch to declare that the patch has been modified. As such, the user
will expect that running "git am --signoff --continue" will append the
signoff to the commit message.

However, the --signoff option is only taken into account during the
mail-parsing stage. If the --signoff option is set, then the signoff
will be appended to the commit message. Since the mail-parsing stage
comes before the patch application stage, the --signoff option, if
provided on the command-line when resuming, will have no effect at all.

We cannot move the append_signoff() call to the patch application stage
as the applypatch-msg hook and interactive mode, which run before patch
application, may expect the signoff to be there.

Fix this by taking note if the user explictly set the --signoff option
on the command-line, and append the signoff to the commit message when
resuming if so.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When resuming, git-am mistakenly ignores command-line options.

For instance, when a patch fails to apply with "git am patch",
subsequently running "git am --3way" would not cause git-am to fall
back on attempting a threeway merge.  This occurs because by default
the --3way option is saved as "false", and the saved am options are
loaded after the command-line options are parsed, thus overwriting
the command-line options when resuming.

Fix this by moving the am_load() function call before parse_options(),
so that command-line options will override the saved am options.

The purpose of supporting this use case is to enable users to "wiggle"
that one conflicting patch. As such, it is expected that the
command-line options do not affect subsequent applied patches. Implement
this by calling am_load() once we apply the conflicting patch
successfully.
Noticed-by: NJunio C Hamano <gitster@pobox.com>
Helped-by: NJunio C Hamano <gitster@pobox.com>
Helped-by: NJeff King <peff@peff.net>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Add the am.threeWay configuration variable to use the -3 or --3way
option of git am by default. When am.threeway is set and not desired
for a specific git am command, the --no-3way option can be used to
override it.
Signed-off-by: NRemi Lespinet <remi.lespinet@ensimag.grenoble-inp.fr>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

At the beginning of the rewrite of git-am.sh to C, in order to not break
existing test scripts that depended on a functional git-am, a
redirection to git-am.sh was introduced that would activate if the
environment variable _GIT_USE_BUILTIN_AM was not defined.

Now that all of git-am.sh's functionality has been re-implemented in
builtin/am.c, remove this redirection, and retire git-am.sh into
contrib/examples/.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When commit_tree() is called, if the user does not have an explicit
committer ident configured, it will attempt to construct a default
committer ident based on the user's and system's info (e.g. gecos field,
hostname etc.) However, if a default committer ident is unable to be
constructed, commit_tree() will die(), but at this point of git-am's
execution, there will already be changes made to the index and work
tree.

This can be confusing to new users, and as such since d64e6b04 (Keep
Porcelainish from failing by broken ident after making changes.,
2006-02-18) git-am.sh will check to see if the committer ident has been
configured, or a default one can be constructed, before even starting to
apply patches.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The -b/--binary option was initially implemented in 087b6742 (git-am:
--binary; document --resume and --binary., 2005-11-16). The option will
pass the --binary flag to git-apply to allow it to apply binary patches.

However, in 2b6eef94 (Make apply --binary a no-op., 2006-09-06), --binary
was been made a no-op in git-apply. Following that, since cb3a160d
(git-am: ignore --binary option, 2008-08-09), the --binary option in
git-am is ignored as well.

In 6c15a1c6 (am: officially deprecate -b/--binary option, 2012-03-13),
the --binary option was tweaked to its present behavior: when set, the
message:

	The -b/--binary option has been a no-op for long time, and it
	will be removed. Please do not use it anymore.

will be printed.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh supported the --interactive mode. After parsing the patch mail
and extracting the patch, commit message and authorship info, an
interactive session will begin that allows the user to choose between:

* applying the patch

* applying the patch and all subsequent patches (by disabling
  interactive mode in subsequent patches)

* skipping the patch

* editing the commit message

Since f89ad67f (Add [v]iew patch in git-am interactive., 2005-10-25),
git-am.sh --interactive also supported viewing the patch to be applied.

When --resolved-ing in --interactive mode, we need to take care to
update the patch with the contents of the index, such that the correct
patch will be displayed when the patch is viewed in interactive mode.

Re-implement the above in builtin/am.c
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 0cfd1120 (am: preliminary support for hg patches, 2011-08-29),
git-am.sh could convert mercurial patches to an RFC2822 mail patch
suitable for parsing with git-mailinfo, and queue them in the state
directory for application.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh was able to auto-detect mercurial
patches by checking if the file begins with the line:

	# HG changeset patch

Re-implement the above in builtin/am.c.
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since c574e683 (git-am foreign patch support: StGIT support, 2009-05-27),
git-am.sh is able to read a single StGit series file and, for each StGit
patch listed in the file, convert the StGit patch into a RFC2822 mail
patch suitable for parsing with git-mailinfo, and queue them in the
state directory for applying.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to auto-detect StGit series
files by checking to see if the file starts with the string:

	# This series applies on GIT commit

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since c574e683 (git-am foreign patch support: StGIT support, 2009-05-27),
git-am.sh supported converting StGit patches into RFC2822 mail patches
that can be parsed with git-mailinfo.

Implement this by introducing two functions in builtin/am.c:
stgit_patch_to_mail() and split_mail_conv().

stgit_patch_to_mail() is a callback function for split_mail_conv(), and
contains the logic for converting an StGit patch into an RFC2822 mail
patch.

split_mail_conv() implements the logic to go through each file in the
`paths` list, reading from stdin where specified, and calls the callback
function to write the converted patch to the corresponding output file
in the state directory. This interface should be generic enough to
support other foreign patch formats in the future.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to auto-detect StGit patches.
Re-implement this in builtin/am.c.
Helped-by: NEric Sunshine <sunshine@sunshineco.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-am.sh will call git-rerere at the following events:

* "git rerere" when a three-way merge fails to record the conflicted
  automerge results. Since 8389b52b (git-rerere: reuse recorded resolve.,
  2006-01-28)

  * Since cb6020bb (Teach --[no-]rerere-autoupdate option to merge,
    revert and friends, 2009-12-04), git-am.sh supports the
    --[no-]rerere-autoupdate option as well, and would pass it to
    git-rerere.

* "git rerere" when --resolved, to record the hand resolution. Since
  f131dd49 (rerere: record (or avoid misrecording) resolved, skipped or
  aborted rebase/am, 2006-12-08)

* "git rerere clear" when --skip-ing. Since f131dd49 (rerere: record (or
  avoid misrecording) resolved, skipped or aborted rebase/am,
  2006-12-08)

* "git rerere clear" when --abort-ing. Since 3e5057a8 (git am --abort,
  2008-07-16)

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh will invoke the post-applypatch hook after the patch is
applied and a commit is made. The exit code of the hook is ignored.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sg will invoke the pre-applypatch hook after applying the patch
to the index, but before a commit is made. Should the hook exit with a
non-zero status, git am will exit.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh will invoke the applypatch-msg hooks just after extracting the
patch message. If the applypatch-msg hook exits with a non-zero status,
git-am.sh abort before even applying the patch to the index.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since eb2151bb (rebase: support automatic notes copying, 2010-03-12),
git-am.sh supported automatic notes copying in --rebasing mode by
invoking "git notes copy" once it has finished applying all the patches.

Re-implement this feature in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 96e19488 (rebase: invoke post-rewrite hook, 2010-03-12), git-am.sh
will invoke the post-rewrite hook after it successfully finishes
applying all the queued patches.

To do this, when parsing a mail to extract its patch and metadata, in
--rebasing mode git-am.sh will also store the original commit ID in the
$state_dir/original-commit file. Once it applies and commits the patch,
the original commit ID, and the new commit ID, will be appended to the
$state_dir/rewritten file.

Once all of the queued mail have been processed, git-am.sh will then
invoke the post-rewrite hook with the contents of the
$state_dir/rewritten file.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3b4e395f (am: add the --gpg-sign option, 2014-02-01), git-am.sh
supported the --gpg-sign option, and would pass it to git-commit-tree,
thus GPG-signing the commit object.

Re-implement this option in builtin/am.c.

git-commit-tree would also sign the commit by default if the
commit.gpgsign setting is true. Since we do not run commit-tree, we
re-implement this behavior by handling the commit.gpgsign setting
ourselves.
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3f01ad66 (am: Add --committer-date-is-author-date option,
2009-01-22), git-am.sh implemented the --committer-date-is-author-date
option, which tells git-am to use the timestamp recorded in the email
message as both author and committer date.

Re-implement this option in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>