git-format-patch should show the correct version

We want to record the version of the tools the patch was generated with.
While these tools could be rebuilt, git-format-patch stayed the same and
report the wrong version.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>