patch applied (ghc): Refactor OccAnal; and improve dead-code elimination

[Simon Peyton Jones]

Wed Mar  5 07:57:08 PST 2008  simonpj at microsoft.com
  * Refactor OccAnal; and improve dead-code elimination
  
  The occurrence analyer is now really rather subtle when dealing
  with recursive groups; see Note [Loop breaking and RULES] especially.
  
  This patch refactors this code a bit, notably 
    * Introduces a new data type Details instead of a tuple
  
    * More clearly breaks up a recursive group into its SCCs
  	before processing it in a separate function occAnalRec
  
    * As a result, does better dead-code elimination, becuause it's
     	done per SCC rather than for the whole Rec
  
  
    
  

    M ./compiler/simplCore/OccurAnal.lhs -59 +86