requiring consistent package dependencies can give surprising results

(Imported from [Trac #511](http://hackage.haskell.org/trac/hackage/ticket/511), reported by guest on 2009-02-27)

I tried running this command:

sudo cabal install test-framework test-framework-hunit test-framework-quickcheck test-framework-quickcheck2

However, Cabal barfed with:

Resolving dependencies...

cabal: cannot configure test-framework-quickcheck-0.2.1. It requires

QuickCheck >=1.1 && <2

For the dependency on QuickCheck >=1.1 && <2 there are these packages:

QuickCheck-1.1.0.0 and QuickCheck-1.2.0.0. However none of them are available.

QuickCheck-1.1.0.0 was excluded because QuickCheck-2.1.0.1 was selected

instead

QuickCheck-1.1.0.0 was excluded because test-framework-quickcheck2-0.2.1

requires QuickCheck >=2.1.0.0

QuickCheck-1.2.0.0 was excluded because QuickCheck-2.1.0.1 was selected

instead

QuickCheck-1.2.0.0 was excluded because test-framework-quickcheck2-0.2.1

requires QuickCheck >=2.1.0.0

This seems to be because the quickcheck and quickcheck2 providers for test-framework by design depend on disjoint versions of `QuickCheck?`. This should not confuse cabal install, since installing the packages sequentially in any order works fine:

sudo cabal install test-framework test-framework-hunit test-framework-quickcheck

sudo cabal install test-framework-quickcheck2