patch applied (ghc-7.0/ghc): Fix an ASSERT failure in FamInstEnv

[Ian Lynagh]

Thu Oct  7 02:13:27 PDT 2010  simonpj at microsoft.com
  * Fix an ASSERT failure in FamInstEnv
  
  I added a lot of comments too, to explain the preconditions;
  esp Note [FamInstEnv]

    M ./compiler/types/FamInstEnv.lhs -20 +47

View patch online:
http://darcs.haskell.org/cgi-bin/darcsweb.cgi?r=ghc-7.0/ghc;a=darcs_commitdiff;h=20101007091327-1287e-2939180a3715022aabb853ae97c6d91d65739f45.gz