[reactive] [PATCH] Checkers to work with QuickCheck-2.3

Hi Conal, I wrote a patch for Checkers to work with QuickCheck-2.3. We can't build Reactive now because Checkers can't be built with QuickCheck-2.3. New QuickCheck has Int and Word instances of Arbitrary and CoArbitrary class. Thus we need to remove the duplicate instances from Checkers. -- Mitsutoshi Aoe maoe.maoe@gmail.com