builtin-commit: remove .git/SQUASH_MSG upon successful commit
builtin-commit: remove .git/SQUASH_MSG upon successful commit

After doing a merge --squash, and commit afterwards, the commit message
template SQUASH_MSG in the git directory is not removed, which means that
the content of SQUASH_MSG is used as default commit message for all
subsequent commits.  So have git commit remove the file SQUASH_MSG from
the git directory upon a successful commit.

The problem was discovered by Frédéric Brière, reported through
 http://bugs.debian.org/464656

Signed-off-by: Gerrit Pape <1b075ba43f4a5dfea44b6cd27eed9c666fd6f389@smarden.org>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git