Catcaches can now store negative entries as well as positive ones, to

speed up repetitive failed searches; per pghackers discussion in late
January.  inval.c logic substantially simplified, since we can now treat
inserts and deletes alike as far as inval events are concerned.  Some
repair work needed in heap_create_with_catalog, which turns out to have
been doing CommandCounterIncrement at a point where the new relation has
non-self-consistent catalog entries.  With the new inval code, that
resulted in assert failures during a relcache entry rebuild.