Proposed change to ForeignPtr

[Manuel M T Chakravarty]

We seem to have a consensus on this one.  We change the type
of the existing functions to

  newForeignPtr :: Ptr a -> FunPtr (Ptr a -> IO ()) -> IO (ForeignPtr a)
  addForeignPtrFinalizer :: ForeignPtr a -> FunPtr (Ptr a -> IO ()) -> IO ()

For GHC, I propose to put the closure-based versions into an
extra module (that's easy enough with the hierarchical
libraries).  This makes changing over old code easier, as it
merely requires to alter the import and not all occurences
of the functions.

Any objections?

Cheers,
Manuel