It turns out that the relcache thinks it can distinguish different

rules and triggers by OID.  So, even though we have no cross-references
in the system catalogs to pg_rewrite.oid or pg_trigger.oid, we'd better
have unique indexes on them.  Put back pg_rewrite_oid_index, which I
mistakenly removed a few days ago, and add pg_trigger_oid_index.