ForeignPtr naming

[Simon Marlow]

> As Haskell finalizers need pre-emptive concurrency, maybe
> they should go somewhere related to concurrency.  Or we
> could have a "Foreign.Concurrent".

Ok, how about Foreign.Concurrent.newForeignPtr and
Foreign.Concurrent.addForeignPtrFinalizer?  i.e. dodging the naming
issue by using the module system.  It also means that code which uses
GHC's existing versions of these functions can be fixed by changing
imports only.

Cheers,
	Simon