Used by the routines at DO_ANY_OBJS_INTERSECT, ADJ_DU_FOR_OBJ_INTERSECT, ADJ_DV_FOR_OBJ_INTERSECT and ADJ_DZ_FOR_OBJ_INTERSECT.

Z set for an empty record, or one with bit 1 of its flags set: the object moving now (ADJ_FOR_OUT_OF_BOUNDS sets it on itself), a lower half while its upper half moves (JOIN_HALVES), or one marked to be passed over, like a sparkle. Knight Lore's is_object_not_ignored.