make commit message a little more consistent and conforting

make commit message a little more consistent and conforting

It is nicer to let the user know when a commit succeeded all the time,
not only the first time.  Also the commit sha1 is much more useful than
the tree sha1 in this case.

This patch also introduces a -q switch to supress this message as well
as the summary of created/deleted files.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>