pgsql: Have autovacuum consider processing TOAST tables separately from

Log Message:
-----------
Have autovacuum consider processing TOAST tables separately from their
main tables.

This requires vacuum() to accept processing a toast table standalone, so
there's a user-visible change in that it's now possible (for a superuser) to
execute "VACUUM pg_toast.pg_toast_XXX".

Modified Files:
--------------
pgsql/src/backend/commands:
vacuum.c (r1.375 -> r1.376)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c?r1=1.375&r2=1.376)
pgsql/src/backend/postmaster:
autovacuum.c (r1.83 -> r1.84)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/autovacuum.c?r1=1.83&r2=1.84)
pgsql/src/backend/tcop:
utility.c (r1.295 -> r1.296)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/utility.c?r1=1.295&r2=1.296)
pgsql/src/include/commands:
vacuum.h (r1.79 -> r1.80)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/vacuum.h?r1=1.79&r2=1.80)