patch applied (ghc): Better cleaning of spills in spill cleaner

[Ben Lippmeier]

Fri Sep 14 02:39:07 PDT 2007  Ben.Lippmeier at anu.edu.au
  * Better cleaning of spills in spill cleaner
  
  Track what slots each basic block reloads from. When cleaning spill 
  instructions we can use this information to decide whether the slot 
  spilled to will ever be read from on this path.

    M ./compiler/nativeGen/RegSpillClean.hs -50 +122