patch applied (ghc-6.8/ghc): EqInst related clean up

[Ian Lynagh]

Thu Sep  6 02:50:18 PDT 2007  Manuel M T Chakravarty <chak at cse.unsw.edu.au>
  * EqInst related clean up
  - Remove some unused and some superflous functions
  - Add comments regarding ancestor equalities
  - Tidied ancestor equality computation
  - Replace some incorrect instToId by instToVar (but there are still some
    bad ones around as we still get warnings with -DDEBUG)
  - Some cleaned up layout
  NB: Code growth is just due to more comments.

    M ./compiler/typecheck/Inst.lhs -5 +4
    M ./compiler/typecheck/TcRnTypes.lhs +11
    M ./compiler/typecheck/TcSimplify.lhs -62 +78
    M ./compiler/typecheck/TcTyFuns.lhs -48 +4
    M ./compiler/typecheck/TcUnify.lhs -2 +2