pgsql: Support syntax "CLUSTER table USING index", which is more

Log Message:
-----------
Support syntax "CLUSTER table USING index", which is more logical.

Holger Schurig

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        cluster.sgml (r1.40 -> r1.41)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/cluster.sgml.diff?r1=1.40&r2=1.41)
    pgsql/src/backend/parser:
        gram.y (r2.586 -> r2.587)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.586&r2=2.587)
    pgsql/src/bin/psql:
        tab-complete.c (r1.160 -> r1.161)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c.diff?r1=1.160&r2=1.161)
    pgsql/src/test/regress/expected:
        cluster.out (r1.17 -> r1.18)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/cluster.out.diff?r1=1.17&r2=1.18)
    pgsql/src/test/regress/sql:
        cluster.sql (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/cluster.sql.diff?r1=1.9&r2=1.10)