Optimization for pickling random states

-- Addresses https://github.com/numpy/numpy/issues/4763
Merge pull request #4768 from depristo/master

ENH: Optimization for pickling random states

the constructor intended for pickling initializes its state via reading /dev/urandom which can be expensive on virtual machines. as the pickle constructor just needs to create any state which will later be initialized these urandom reads are unnecessary.