patch applied (ghc): Fix and improve deriving for indexed data types

[chak at cse.unsw.edu.au]

Wed Jan  3 17:31:56 PST 2007  Manuel M T Chakravarty <chak at cse.unsw.edu.au>
  * Fix and improve deriving for indexed data types
  - The test for being able to derive the requested classes needs to be made
    with the representation tycon (not the family tycon).
  - Standalone deriving for indexed types requires the instance types in the
    derive clause to match a data/newtype instance exactly (modulo alpha).

    M ./compiler/typecheck/TcDeriv.lhs -25 +35
    M ./compiler/typecheck/TcEnv.lhs -5 +13
    M ./compiler/types/FamInstEnv.lhs -46
    M ./compiler/types/Type.lhs -1 +8