git-commit: do not muck with commit message when no_edit is set.

Spotted by Linus and Darrin Thompson.  When we took a commit
message from -F <file> with an incomplete line, we appended "git
status" output, which ended up attaching a lone "#" at the end.

We still need the "do we have anything to commit?" check by
running "status" (which has to know what to do in different
cases with -i/-o/-a), but there is no point appending its output
to the proposed commit message given by the user.

Signed-off-by: Junio C Hamano <junkio@cox.net>