Complete the evidence generation for GADTs

Complete the evidence generation for GADTs
Mon Sep 18 14:43:22 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Complete the evidence generation for GADTs
  Sat Aug  5 21:39:51 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * Complete the evidence generation for GADTs
    Thu Jul 13 17:18:07 EDT 2006  simonpj@microsoft.com

      This patch completes FC evidence generation for GADTs.

      It doesn't work properly yet, because part of the compiler thinks
      	(t1 :=: t2) => t3
      is represented with FunTy/PredTy, while the rest thinks it's represented
      using ForAllTy.  Once that's done things should start to work.