Fix type checking of imported data instances

Fix type checking of imported data instances
Mon Sep 18 19:48:41 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Fix type checking of imported data instances
  Mon Sep 11 20:06:51 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * Fix type checking of imported data instances
    - When reading a data/newtype instance from an interface, the data constructors
      have their own universals that do not necessarily match up with their tycon's
      type parameters.  (Whereas when type checking source, they are always the
      same.)
    - Hence, we need to be careful when building the wrapper signature of imported
      data constructors from data/newtype instances, and rename the type variables
      in the instance types appropriately.