patch applied (ghc): Big tidy-up of deriving code

Tue Jan  2 07:46:10 PST 2007  [email protected]
  * Big tidy-up of deriving code
  
  This tidy-up, triggered by Trac #1068, re-factors the way that 'deriving' 
  happens.  It took me way longer than I had intended.  The main changes,
  by far are to TcDeriv; everyting else is a minor consequence.
  
  While I was at it, I changed the syntax for standalone deriving, so that
  it goes
  	derive instance Show (T a)
  
  (instead of "derive Show for T").  However, there's still an implicit
  context, generated by the deriving code, and I wonder if it shouldn't really
  be
  	derive instance (..) => Show (T a)
  but I have left it simple for now.
  
  I also added a function Type.substTyVars, and used it here and there, which
  led to some one-line changes otherwise unrelated (sorry).
  
  Loose ends:
    * 'deriving Typeable' for indexed data types is still not right
    * standalone deriving should be documented
  

    M ./compiler/basicTypes/DataCon.lhs -1 +1
    M ./compiler/basicTypes/MkId.lhs -1 +1
    M ./compiler/hsSyn/HsDecls.lhs -10 +21
    M ./compiler/hsSyn/HsTypes.lhs -2 +1
    M ./compiler/hsSyn/HsUtils.lhs +2
    M ./compiler/parser/Lexer.x -3 +3
    M ./compiler/parser/Parser.y.pp -6 +3
    M ./compiler/rename/RnSource.lhs -4 +3
    M ./compiler/typecheck/Inst.lhs -1 +1
    M ./compiler/typecheck/TcDeriv.lhs -335 +342
    M ./compiler/typecheck/TcEnv.lhs -8 +17
    M ./compiler/typecheck/TcExpr.lhs -1 +1
    M ./compiler/typecheck/TcGenDeriv.lhs -2 +1
    M ./compiler/typecheck/TcHsType.lhs -10 +23
    M ./compiler/typecheck/TcInstDcls.lhs -5 +1
    M ./compiler/typecheck/TcMType.lhs -1 +1
    M ./compiler/typecheck/TcSimplify.lhs -46 +15
    M ./compiler/typecheck/TcType.lhs -1 +1
    M ./compiler/types/FamInstEnv.lhs -3 +7
    M ./compiler/types/TyCon.lhs -3 +3
    M ./compiler/types/Type.lhs -2 +4
    M ./compiler/utils/Util.lhs -1 +8