Just before updating a ref,
$GIT_DIR/hooks/update refname old-sha1 new-sha1
is called if executable. The hook can decline the ref to be
updated by exiting with a non-zero status, or allow it to be
updated by exiting with a zero status. The mechanism also
allows e.g sending of a mail with pushed commits on the remote
repository.
Documentation update with an example hook is included.
jc: The credits of the basic idea and initial implementation go
to Josef, but I ended up rewriting major parts of his patch, so
bugs are all mine. Also I changed the semantics for the hook
from his original version (which were post-update hook) so that
the hook can optionally decline to update the ref, and also can
be used to implement the overall cleanups. The latter was
primarily to implement a suggestion from Linus that calling
update-server-info should be made optional.
Signed-off-by: Junio C Hamano <junkio@cox.net>
