pgsql: Update autovacuum to use reloptions instead of a system catalog,

Log Message:
-----------
Update autovacuum to use reloptions instead of a system catalog, for
per-table overrides of parameters.

This removes a whole class of problems related to misusing the catalog,
and perhaps more importantly, gives us pg_dump support for the parameters.

Based on a patch by Euler Taveira de Oliveira, heavily reworked by me.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        catalogs.sgml (r2.196 -> r2.197)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml?r1=2.196&r2=2.197)
        config.sgml (r1.206 -> r1.207)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.206&r2=1.207)
        maintenance.sgml (r1.89 -> r1.90)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/maintenance.sgml?r1=1.89&r2=1.90)
    pgsql/doc/src/sgml/ref:
        alter_table.sgml (r1.102 -> r1.103)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/alter_table.sgml?r1=1.102&r2=1.103)
        create_table.sgml (r1.112 -> r1.113)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_table.sgml?r1=1.112&r2=1.113)
    pgsql/src/backend/access/common:
        reloptions.c (r1.20 -> r1.21)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.20&r2=1.21)
    pgsql/src/backend/catalog:
        Makefile (r1.68 -> r1.69)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/Makefile?r1=1.68&r2=1.69)
    pgsql/src/backend/postmaster:
        autovacuum.c (r1.92 -> r1.93)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/autovacuum.c?r1=1.92&r2=1.93)
    pgsql/src/include/catalog:
        catversion.h (r1.521 -> r1.522)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.521&r2=1.522)
        indexing.h (r1.106 -> r1.107)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/indexing.h?r1=1.106&r2=1.107)
    pgsql/src/include/utils:
        rel.h (r1.111 -> r1.112)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/rel.h?r1=1.111&r2=1.112)
    pgsql/src/test/regress/expected:
        sanity_check.out (r1.38 -> r1.39)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/sanity_check.out?r1=1.38&r2=1.39)

Removed Files:
-------------
    pgsql/src/include/catalog:
        pg_autovacuum.h
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_autovacuum.h)