Typing f.e.d.

[Simon Marlow]

> As usual the FFI "looks through" newtypes.  But now that we have
> FunPtr, the following typing makes much more sense:
> 
>    'foreign' 'export' [callconv] 'dynamic' varid :: prim_type 
> -> IO (FunPtr prim_type)
> 
> where both prim_types have to be the *same*. We should probably allow
> the old Addr-typing as well for some time to facilitate the 
> transition,
> but not the Ptr-typing (bleeding edge people will know what to do :-).
> The corresponding changes to GHC look easy, so I'd like to commit this
> if there are no objections.

Sounds reasonable to me.

Simon