Always have pg_dump write rules in a consistent order

Hi,

When working on a new feature for PostgreSQL I noticed that the
pg_upgrade tests became flaky due to rules being dumped in a different
order between the original cluster and the upgraded cluster. (For
context: my regress scripts left a bunch of views with dependency
circles which I had forgot to clean up.)

So I propose that we sort rules on (schema, name, relation_name) instead
of (schema, name, oid) like it currently does. The patch itself is small
enough and makes it easier to test that we upgrade rules and views
correctly with pg_upgrade.

Andreas