Add a testPropertyFor to {hunit,tasty}-dejafu

[barrucadu]

There's a testProperty, which uses check', but nothing exposing checkFor. Something like this:

-- | Like testProperty, but takes a number of cases to check.
--
-- The maximum number of cases tried by @testPropertyFor n m@ will be @n * m@.
testPropertyFor :: (R.Testable p, R.Listable (R.X p), Eq (R.X p), Show (R.X p), Show (R.O p))
  => Int
  -- ^ Number of seed values per variable-assignment.
  -> Int
  -- ^ Number of variable assignments.
  -> String
  -- ^ The name of the test.
  -> p
  -- ^ The property to check.
  -> Test