QuickCheck is missing Arbitrary instances for fixed-size integral types

[John Millikin]

The 'Data.Int' and 'Data.Word' modules in 'base' define several
fixed-size integral types (Int8-Int64, Word8-Word64). QuickCheck does
not define Arbitrary instances for these. It'd be pretty easy to
include them in QuickCheck, which would make client code less fragile
(since it won't have to define orphan instances).

There's a function already defined in 'Test.QuickCheck.Arbitrary'
which can be used -- just redefine 'arbitrarySizedBoundedInt' as:

	arbitrarySizedBoundedIntegral :: (Bounded a, Integral a) => Gen a
	arbitrarySizedBoundedIntegral =
	    # .. function body remains the same ..

and add the following instances:

	import Data.Int
	import Data.Word

	instance Arbitrary Int8 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Int16 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Int32 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Int64 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Word where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Word8 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Word16 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Word32 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

	instance Arbitrary Word64 where
		arbitrary = arbitrarySizedBoundedIntegral
		shrink    = shrinkIntegral

Thanks!