Makes the IR much easier to follow.  Also I think the plan will be
to have the cxx unwinder do the refcounting.

(if the variable is defined before then)
otherwise we would try to incref the variable before guards which would fail the rewrite.

(At least, the ones that we referenced statically.)

Amazing that it didn't end up showing up until now.

to explicitly represent exceptional control flow, so that we can put refcounting
operations on it.

WIP on adding refcounts.  I think this will be quite a bit more complicated because we have to change the exception control flow to add decrefs

And source it after loading the pyston executable.

Need to make setattr() stealing

xdecref is a fair bit slower than decref (especially as it's implemented right
now as a helper function), but I think this will be ok once we get the llvm
jit up and running with refcounting.