pgsql: Disallow setting fillfactor for TOAST tables.

Log Message:
-----------
Disallow setting fillfactor for TOAST tables.

To implement this without almost duplicating the reloption table, treat
relopt_kind as a bitmask instead of an integer value.  This decreases the
range of allowed values, but it's not clear that there's need for that much
values anyway.

This patch also makes heap_reloptions explicitly a no-op for relation kinds
other than heap and TOAST tables.

Patch by ITAGAKI Takahiro with minor edits from me.  (In particular I removed
the bit about adding relation kind to an error message, which I intend to
commit separately.)

Modified Files:
--------------
    pgsql/src/backend/access/common:
        reloptions.c (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.24&r2=1.25)
    pgsql/src/include/access:
        reloptions.h (r1.13 -> r1.14)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/reloptions.h?r1=1.13&r2=1.14)