Add nqp:: ops for runtime variable lookup.
Add nqp:: ops for runtime variable lookup.

If you're building a QAST tree up, QAST::Var is just fine. But for
lookups where we don't know what we want until runtime, or to write
in NQP code, these are useful.

cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp