BUG: reject too large seeds to RandomState

mtrand accepts seeds larger than 32 bit but silently truncates them back
to 32 bit. This can lead to accidentally getting the same random stream
for two different seeds, e.g. 1 and 1 + 2**40.
Merge pull request #4676 from juliantaylor/rand-seed-lim

BUG: reject too large seeds to RandomState