pgsql: Use more-portable coding for the check on handing out the last

Log Message:
-----------
Use more-portable coding for the check on handing out the last available
relopt_kind value in add_reloption_kind().  Per Zdenek Kotala.

Modified Files:
--------------
    pgsql/src/backend/access/common:
        reloptions.c (r1.26 -> r1.27)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.26&r2=1.27)
    pgsql/src/include/access:
        reloptions.h (r1.14 -> r1.15)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/reloptions.h?r1=1.14&r2=1.15)