pgsql: Remove contrib/intarray's definitions of the <@ and @> operators,

Log Message:
-----------
Remove contrib/intarray's definitions of the <@ and @> operators, so that they
don't cause confusion with the built-in anyarray versions of those operators.
Adjust the module's index opclasses to support the built-in operators in place
of the private ones.

The private implementations are still available under their historical
names @ and ~, so no functionality is lost.  Some quick testing suggests
that they offer no real benefit over the core operators, however.

Per a complaint from Rusty Conover.

Modified Files:
--------------
    pgsql/contrib/intarray:
        _int.sql.in (r1.29 -> r1.30)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/intarray/_int.sql.in?r1=1.29&r2=1.30)
        uninstall__int.sql (r1.10 -> r1.11)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/intarray/uninstall__int.sql?r1=1.10&r2=1.11)
    pgsql/doc/src/sgml:
        intarray.sgml (r1.6 -> r1.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/intarray.sgml?r1=1.6&r2=1.7)