addForeignPtrFinalizer

[Alastair Reid]

> Then I'll reformulate my question as a patch. [...]
> Is there anything fundamentally wrong with this approach?

I still maintain that getting this to work, testing it and,
especially, maintaining it is a lot of work.  [For example, you
mention that finalizers that point to the object they finalize don't
work.  I guess we could fix that by adding GHC-style WeakPtrs.]

I don't think it's appropriate to add that burden just so we can call
free at the right time.  We have a simple problem, there should be a
simple solution.

A