Add (untested so far) capturelex op.
Minimal changes to cope with declaration_static.

Not actually generating code any differently yet.
Sync closure NQP changes into our copy of NQP.
Switch QAST -> MAST to new closure model.

This should hopefully eliminate dependence on prior_invocation.
Remove prior_invocation hack.

This yields 7 new failures in selftest, which will need tracking
down.
Some declaration_static fixes from NQP repo.
Remove dead decl.
Re-instate error check; prevents SEGVs.
Set ->static_code in StaticFrame in bytecode load.
Fix cloned onlystar protoregex case.

This unbusts 55-multi-method.t.
Fix correct-outer test.
MAIN fix from NQP.
Contextual leak prevention.
Toss looking down the stack for outer.

This was a fallback, but it turns out we depended on it a lot. Now we
barely do, so it can go away. We will need a proper auto-close for a
handful of rare cases, but removing this approximation of it shows up
a couple of places we wrongly depend on such a thing, that need fixes
before putting auto-close in.
Make multi subs not depend on auto-close.

Technically, still not quite right, but no worse than before.
First pass at autoclose.

24-module.t now passes.
Greatly simplify rethrow implementation.

Has added advantage of not placing the PC in a random place after the
unwind, though I'm not entirely sure how that was happening before. :)
According to test suite, shouldn't cache envhash.
envhash values should be boxed.
Missing MVMROOTs.