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.