Argh, got typo into the bootstrap. :(
Implement nqp::invokewithcapture.
Switch over to using the new multi-dispatch code.

With it, we get a working NQP that passes its tests. However, it's a
good bit slower since caching hasn't been restored yet.
Add ops for working directly with multi cache.
Avoid serializing the dispatch sort order.

Otherwise every module does and we get conflicts.
Update bootstrap.
Reinstate multi-dispatch cache after refactors.