Qualify table usage in dumpTable() and use regclass

Qualify table usage in dumpTable() and use regclass

All of the other tables used in the query in dumpTable(), which is
collecting column-level ACLs, are qualified, so we should be qualifying
the pg_init_privs, the related sub-select against pg_class and the
other queries added by the pg_dump catalog ACLs work.

Also, use ::regclass (or ::pg_catalog.regclass, where appropriate)
instead of using a poorly constructed query to get the OID for various
catalog tables.

Issues identified by Noah and Alvaro, patch by me.