[project @ 2004-02-25 13:54:30 by simonpj]

Yet another fix to the -Onot optimisation that hides data type
representations in .hi files.

1.  Expose the representation if any fields are exposed

2.  Don't expose newtypes whose data-cons are abstract, unless the
    rep type is a FFI type.  (Previously we were more conservative
    and always exposed newtypes, just in case of a foreign decl.)