Add some appropriate nyi warnings for :: and :::, rather than silently failing.
Add some appropriate nyi warnings for :: and :::, rather than
silently failing.

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