patch applied (cabal-install): Take preferred versions into account in dependency planning

[Duncan Coutts]

Sun Oct  5 22:51:29 PDT 2008  Duncan Coutts <duncan at haskell.org>
  * Take preferred versions into account in dependency planning
  This means we can now globally prefer base 3 rather than 4.
  However we need to be slightly careful or we end up deciding
  to do silly things like rebuild haskell98 against base 3.
  That would happen because the h98 package doesn't constrain
  the choice to one or the other and we would prefer base 3.
  So we have to add that we really prefer whatever it uses
  currently (if any).

    M ./Distribution/Client/Dependency/TopDown.hs -12 +30

View patch online:
http://darcs.haskell.org/cabal-install/_darcs/patches/20081006055129-adfee-7e291402171fca8c8796efa44a1f9c55d309d090.gz