patch applied (ghc): Fix a bug in rule matching

[Simon Peyton Jones]

Thu May  4 04:24:30 PDT 2006  simonpj at microsoft.com
  * Fix a bug in rule matching
  
  The rule matcher uses a "rough-match" pre-filter, which was being too 
  aggressive.  The case looked like this:
  
  	rule:	f True
  	expr:	case e of x { True -> f x }
  
  Jues because x doesn't immediately look like True, we shouldn't say
  "can't match", but that is exactly what ruleCantMatch was doing.
  
  

    M ./compiler/specialise/Rules.lhs -5 +10