patch applied (ghc): Make eta reduction check more carefully for bottoms (fix Trac #1947)

[Simon Peyton Jones]

Tue Dec  4 06:58:03 PST 2007  simonpj at microsoft.com
  * Make eta reduction check more carefully for bottoms (fix Trac #1947)
  
  Eta reduction was wrongly transforming
  	f = \x. f x
  to
  	f = f
  
  Solution: don't trust f's arity information; instead look at its
  unfolding.  See Note [Eta reduction conditions]
  
  Almost all the new lines are comments!
  
  

    M ./compiler/simplCore/SimplUtils.lhs -23 +75