Allow IO to be wrapped in a newtype in foreign import/export

Allow IO to be wrapped in a newtype in foreign import/export

Up to now, the silent unwrapping of newtypes in foreign import/export
has been limited to data values.  But it's useful for the IO monad
itself:

	newtype MyIO a = MIO (IO a)

	foreign import foo :: Int -> MyIO Int

This patch allows the IO monad to be
wrapped too. This applies to foreign import "dynamic" and "wrapper",
thus
   foreign import "wrapper" foo :: MyIO () -> HisIO (FunPtr (MyIO ()))

Warning: I did on the plane, and I'm no longer sure if its 100%
complete, so needs more testing.  In particular the wrapper/dynamic bit.