patch applied (cabal): Export Command constructor so cabal-install can make derived commands

[Duncan Coutts]

Sat Dec  8 11:24:01 PST 2007  Duncan Coutts <duncan at haskell.org>
  * Export Command constructor so cabal-install can make derived commands
  Also move commandHelp out of the structure into a helper function. Change
  the type of commandOptions so it doesn't include the CommonFlag. Instead,
  add those in whenever necessary. This makes deriving commands easier.
  Also fix docs.

    M ./Distribution/Simple/Command.hs -13 +17