Fix lots of bugs relating to store refcounting around loops and handling global variables.
Lots of misc fixes, more tests pass again
More misc fixes, plus disable invariant edge evaluation since now the loop fixpoint analysis can find them it's not worth very much and confuses the bookkeeping, since the marker for invariant-dead looks the same as that for fixpoint-dead.
Lots more fixes including rewriting the subvalue-extraction paths to use a shared, more powerful algorithm that can pull multiple valsets out of a composite, and fix several problems in the globals and memcpy paths.