Issue 630/1: Implement Grob_property_info::matched_pop

Issue 630/1: Implement Grob_property_info::matched_pop

This can be passed a token returned from Grob_property_info::push and
will then only revert the matching push or nothing at all.  This is used
to limit the fallout from internal property reversions that might not
match the original override because of an intervening property push/pop.