This mimics what TranslatorX64 does in translateSetMArray,
but it does it with fewer helpers and (often) fewer instructions in
translated code. I also found a bug in both jits and the interpreter
when dealing with arrays that hold refs to themselves. The new test
case exercises the fix, which involved a bit of refactoring of the
refcounting logic.
Enabling VectorTranslator while punting to tx64 is no longer a
regression so I removed the punt in emit().
bsimmers
ea56a8383e