patch applied (cabal): Add new Command abstraction for handling command line args

[Duncan Coutts]

Fri Nov 16 06:12:25 PST 2007  Duncan Coutts <duncan at haskell.org>
  * Add new Command abstraction for handling command line args
  Add instances of it for all existing Cabal commands.
  This should makes command line handling more regular and hopefully make it
  easier to override or make derived commands in cabal-install.
  So far we're only adding code, not modifying existing stuff except renaming
  some existing internal functions so they do not clash with the new code.

    A ./Distribution/Simple/Command.hs
    M ./Distribution/Simple/Setup.hs -13 +542