patch applied (ghc): Add deShadowBinds

[Simon Peyton Jones]

Mon May 22 12:24:04 PDT 2006  simonpj at microsoft.com
  * Add deShadowBinds
  
  Add CoreSubst.deShadowBinds, which removes shadowing from 
  a Core term.  I thought we wanted it for SpecConstr, but in 
  fact decided not to use it. Nevertheless, it's a useful sort
  of function to have around, and it has a particularly simple
  definition!
  

    M ./compiler/coreSyn/CoreSubst.lhs -10 +28