format-patch: Add "--no-stat" as a synonym for "-p"

format-patch: Add "--no-stat" as a synonym for "-p"

"-p" means "generate patch" in 'git log' and 'git diff', so it's
quite surprising that it means "suppress diffstat" in
'git format-patch'.

Keep the "-p" option for backward compatibility, but add
"--no-stat" as a more intuitive synonym. For backward compatibility
with scripts, we must allow combinations of --stat and --no-stat.

Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>