GCC's format __attribute__ is good for checking errors, especially
with -Wformat=2 parameter. This fixes most of the reported problems
against 2005-08-09 snapshot.

It always uses a git-relative pathname, ie "refs/heads/master" instead of
".git/refs/heads/master" or whatever your GIT_DIR might be.

This way when we send refs back-and-forth between repositories, there's
never any question about GIT_DIR on either side.

It did a "for_each_ref()" in addition to the HEAD case, which was a
left-over from an early broken test.

"git_path()" returns a static pathname pointer into the git directory
using a printf-like format specifier.

"head_ref()" works like "for_each_ref()", except for just the HEAD.

Remove the "./" at the head, it just looks much nicer.

It needed to take the GIT_DIR information into account, something that
the original receive-pack usage just never cared about.

This turns it into a generic "do xyz for each ref" library function.

This patch adds code to read a hash out of a specified file under
{GIT_DIR}/refs/, and to write such files atomically and optionally with an
compare and lock.
Signed-off-by: NDaniel Barkalow <barkalow@iabervon.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>