patch applied (ghc): FIX: TypeFamilies: should_compile/Simple12

[chak at cse.unsw.edu.au]

Sun Sep 16 06:04:19 PDT 2007  Manuel M T Chakravarty <chak at cse.unsw.edu.au>
  * FIX: TypeFamilies: should_compile/Simple12
  - checkTauTvUpdate now distinguishes between whether
    (1) a type variables occurs only in type family parameters
        (in which case unification is to be deferred)
    (2) other variable occurences
        (which case we fail with a cannot create infinite type message, as before)

    M ./compiler/typecheck/TcMType.lhs -25 +106
    M ./compiler/typecheck/TcTyFuns.lhs -4 +8
    M ./compiler/typecheck/TcUnify.lhs -33 +22