patch applied (ghc-6.8/ghc): FIX Trac #1935: generate superclass constraints for derived classes

[Ian Lynagh]

Wed Nov 28 07:05:41 PST 2007  simonpj at microsoft.com
  * FIX Trac #1935: generate superclass constraints for derived classes
  
  This bug only reports a problem with phantom types, but actually
  there was quite a long-standing and significant omission in the
  constraint generation for derived classes.  See
  Note [Superclasses of derived instance] in TcDeriv.
  
  The test deriving-1935 tests both cases.
  
  

    M ./compiler/typecheck/TcDeriv.lhs -4 +31