[computer-go] C++ random numbers

[Chris Fant]

> The checks I do for repeated numbers are actually stricter than if using
> a 64 bit integer, as it requires both high and low halves to
> be unique. I suspect this is good (less chance of two different
> positions having the same hash code), but otherwise it makes no difference.
> If it was good then it'd be worth generating 16 bit numbers and check
> their uniqueness, then combining them to make the 32 bit numbers.

Be careful with this sort of thing.  The "smarter" you are, the less
random you are.

I also use a Mersenne Twister RNG.