It turns out that the relcache thinks it can distinguish different

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.