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

[Mitsutoshi Aoe]

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...@gmail.com