introduce "default_use_oids" - Mailing list pgsql-patches

This patch adds a new GUC var, "default_use_oids", which follows the
proposal for eventually deprecating OIDs on user tables that I posted
earlier to pgsql-hackers. pg_dump now always specifies WITH OIDS or
WITHOUT OIDS when dumping a table. The documentation has been updated.

Comments are welcome.

(This patch is for the 7.5 queue.)

-Neil