I was noticing that classes were getting freed a few
collections after they were seen to be not-marked; the
issue with the old keep-classes-alive implementation is
that it assumed that !isMarked() implies that the object
will be freed in the sweep phase.  With the finalization
ordering, this isn't true.  We could move the ordering
before the keep-classes-alive behavior, but then the
finalization ordering might get things wrong since it
wouldn't see the final set of mark bits.  So I think
we need to integrate the two phases.

I think it ends up working to just say that type objects
have ordered finalizers, even though they typically don't;
I think this gets us the guarantees we need.