commit: search author pattern against mailmap
"git commit --author=$name" sets the author to one whose name
matches the given string from existing commits, when $name is not in
the "Name <e-mail>" format. However, it does not honor the mailmap
to use the canonical name for the author found this way.
Fix it by telling the logic to find a matching existing author to
honor the mailmap, and use the name and email after applying the
mailmap.
Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>