Some time ago we changed git-log in a massive way, and one consequence is
that the keyword changed. Adjust patch-id for that.

[jc: as Linus suggests, allowing both old and new prefix.]
Signed-off-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Do our own ctype.h, just to get the sane semantics: we want
locale-independence, _and_ we want the right signed behaviour. Plus we
only use a very small subset of ctype.h anyway (isspace, isalpha,
isdigit and isalnum).
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Two else equal patches should not result in different checksums, only
because they were applied to different versions of the file.
Signed-off-by: NKai Ruemmler <kai.ruemmler@gmx.net>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

The *_usage strings should not start with "usage: ", since the
usage() function gives its own.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

A "patch ID" is nothing but a SHA1 of the diff associated with a patch,
with whitespace and line numbers ignored.  As such, it's "reasonably
stable", but at the same time also reasonably unique, ie two patches
that have the same "patch ID" are almost guaranteed to be the same
thing.

IOW, you can use this thing to look for likely duplicate commits.