Packages that split hackage

[Duncan Coutts]

I've been trying to make a consistent set of packages to test releases
of Cabal and cabal-install.

What I've noticed is that there are a small number of packages that
almost cut hackage down the middle. 

At the moment the main culprit is
QuickCheck 1 vs 2
Whichever version you pick, you exclude a large swath of packages.

The other notable ones are

HaXml 1.13 vs 1.19
parsec 2 vs 3

haskell-src-exts, lots of packages depend (directly or indirectly) on
various incompatible 1.x versions.

I'm now doing three builds of 1453 packages from hackage, using:
      * cabal-install-0.6.2 (baseline)
      * cabal-install-0.6.3 (dev version of stable branch)
      * cabal-install-0.7.5 (dev version of head branch)

Duncan