patch applied (cabal-install): Rearange install plan checking code

[Duncan Coutts]

Thu Apr 24 15:41:59 PDT 2008  Duncan Coutts <duncan at haskell.org>
  * Rearange install plan checking code
  Make it usable for callers that want to check
  properties before constructing an InstallPlan.

    M ./Hackage/InstallPlan.hs -51 +52

View patch online:
http://darcs.haskell.org/cabal-install/_darcs/patches/20080424224159-adfee-2da463f44d1a9c82fde16e9816aeaf67fb46cfe1.gz