make subrule_alias a method, so that subclasses can reuse it easily
make subrule_alias a method, so that subclasses can reuse it easily

cygx/nqp,perl6/nqp-rx,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,perl6/nqp-rx,cygx/nqp,cygx/nqp