Move refspec pattern matching to match_refs().

Move refspec pattern matching to match_refs().

This means that send-pack and http-push will support pattern refspecs,
so builtin-push.c doesn't have to expand them, and also git push can
just turn --tags into "refs/tags/*", further simplifying
builtin-push.c

check_ref_format() gets a third "conditionally okay" result for
something that's valid as a pattern but not as a particular ref.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>