pgsql: Ensure default-only storage parameters for TOAST relations to be

Log Message:
-----------
Ensure default-only storage parameters for TOAST relations
to be initialized with proper values. Affected parameters are
fillfactor, analyze_threshold, and analyze_scale_factor.

Especially uninitialized fillfactor caused inefficient page usage
because we built a StdRdOptions struct in which fillfactor is zero
if any reloption is set for the toast table.

In addition, we disallow toast.autovacuum_analyze_threshold and
toast.autovacuum_analyze_scale_factor because we didn't actually
support them; they are always ignored.

Report by Rumko on pgsql-bugs on 12 May 2010.
Analysis by Tom Lane and Alvaro Herrera. Patch by me.

Backpatch to 8.4.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        create_table.sgml (r1.127 -> r1.128)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_table.sgml?r1=1.127&r2=1.128)
    pgsql/src/backend/access/common:
        reloptions.c (r1.34 -> r1.35)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.34&r2=1.35)
    pgsql/src/bin/psql:
        tab-complete.c (r1.198 -> r1.199)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c?r1=1.198&r2=1.199)