Random.jumpahead deprecated in Python 3

The jumpahead method for random.Random no longer exists in Python 3 as
it was unsafe with the Mersenne Twister RNG. Simply creating a new
instance of random.Random (without a seed) suffices for creating
independent state (jumpahead was unnecessary). No results should be
affected: without setting a random seed or time_dependent=True there is
no meaningful notion of reproducible streams to worry about.