patch applied (ghc): Retain simplifications of implication constraints

[Simon Peyton Jones]

Wed Nov 22 05:28:44 PST 2006  simonpj at microsoft.com
  * Retain simplifications of implication constraints
  
  When simplifying an implication constraint (reduceImplication), if we make
  progress, make a new implication constraint for the result.  If we don't
  do this, we get a constraint that can be simplified in a unique way,
  and that in turn confuses reportNoInstance
  

    M ./compiler/typecheck/TcRnTypes.lhs -1 +2
    M ./compiler/typecheck/TcSimplify.lhs -51 +62