0.3 replaced random-source with the normal random package, so we can now
use a more portable globalStdGen fro Data.Random.Show.Unsafe.

We lose the dependency on random-source and incur one on random. The
lower bound on random-fu is increased.

Closes #4.

fix Data.Random.Shuffle.Weighted in corner cases (except integral weights, which still produce the wrong distribution, to be done)