(1) Pref now has non_generalizable flags for id, att, value and referent
(2) Make_fake_instantiation sets non-var flags of conds rhs prefs, also caches grounding wme in identity of conds
(3) Smem's call to chunk_instantiation now repropagates identities
(4) get_ground_id returns non_generalizable if no preference exists or if non_generalizable flag set in preference
(5) Fixed crash by stopping add_identity_to_negative_test from setting grounding identity for non_generalizable tests