architecture-dependent types

[Simon Marlow]

> Should not Foreign.C.Types, Foreign.C.TypesISO and System.Posix.Types
> export their types opaquely?  That would make their interface and
> documentation architecture-independent.

The FFI doesn't explicitly specify whether these types should be
exported abstractly or not, but it does say in section 6.2:

"... all types exported by \code{CTypes} are
represented as type synonyms or \code{newtype}s of basic foreign types
..."

we should really decide one way or the other, since this ambiguity will
lead to non-portable differences between implementations of CTypes (and
hence Foreign.C.Types).  

Having the types be opaque sounds reasonable to me, and similarly for
System.Posix.Types.

Cheers,
	Simon