mesa/dlist: fixes and improvements for material caching

mesa/dlist: fixes and improvements for material caching

Only short-circuit material call if *all* statechanges from this call
are cached.  Some material calls (eg with FRONT_AND_BACK) change more
than one piece of state -- need to check all of them before returning.

Also, Material calls are legal inside begin/end pairs, so don't need
to be as careful about begin/end state as with regular statechanges
(like ShadeModel) when caching.  Take advantage of this and do better
caching.