rename "match_refs()" to "match_push_refs()"

rename "match_refs()" to "match_push_refs()"

Yes, there is a warning that says the function is only used by push in big
red letters in front of this function, but it didn't say a more important
thing it should have said: what the function is for and what it does.

Rename it and document it to avoid future confusion.

Signed-off-by: Junio C Hamano <gitster@pobox.com>