Currently when format-patch is used with --attach or --inline the patch
attachment has the SHA1 of the commit for its filename. This replaces
the SHA1 with the filename used by format-patch when outputting to
files.
Fix tests relying on the SHA1 output and add a test showing how the
--suffix option affects the attachment filename output.
Signed-off-by: Stephen Boyd <bebarino@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>