patch applied (ghc): Allow -ddump-simpl-phases to specify which phases to dump

[Roman Leshchinskiy]

Sun Feb 10 18:06:30 PST 2008  Roman Leshchinskiy <rl at cse.unsw.edu.au>
  * Allow -ddump-simpl-phases to specify which phases to dump
  
  We can now say -ddump-simpl-phases=1,2 to dump only these two phases and
  nothing else.

    M ./compiler/coreSyn/CoreLint.lhs -1 +4
    M ./compiler/main/DynFlags.hs -2 +34
    M ./compiler/main/ErrUtils.lhs -6 +12
    M ./compiler/simplCore/SimplCore.lhs -5 +8