RE: Core, shadowing type variable names, possible fix

| I have found what causes the bug and implemented a possibly 
| fix for it. 
| The problem has to do with source types that aren't expanded before 
| tidying them.

Quite right.  Well found.  
| I believe that there are three possible fixes:
| 
|   1. Make sure that all type variables that are bound in non 
| recursive 
| newtypes are made unique
|   2. Expand all non recursive newtypes before using tidyXXX
|   3. Not expand the non recursive newtypes when generating 
| external core
| 
| 
| I have implemented the third alternative.

Yes, that looks fine.  I think we'd better update the External Core
documentation about newtypes too (in ghc/docs/ext-core/core.tex).  If
you felt like adding anything to it, go ahead; or else I will sometime.

Simon