Provide some HLL config infrastructure.

This will allow creating correct box types and slurpy array/hash types
in NQP, but using the BOOT types in NQP's MOP until the others are
made available.
Test for slurpy positional arguments.
Code-gen for slurpy params.
Fix a GlobalContext build-up bug.
Implement posslurpy op.

Positional slurpy params now work.