Re: gaussian distribution pgbench -- splits v4

Maybe somebody who knows more math than I do (like you, probably!) can come up with something more clever.

I can certainly suggest other formula, but that does not mean beautiful code, thus would probably be rejected. I'll see.

An alternative to this whole process may be to hash/modulo a non uniform random value.

      id = 1 + hash(some-random()) % n

But the hashing changes the distribution as it adds collisions, so I have to think about how to be able to control the distribution in that case, and what hash function to use.