class SplittableRandom

[Doug Lea]

After exploring a bunch of algorithmic variants, we committed to
one of the simplest for consideration for inclusion in JDK8.
Thanks again to everyone sending comments and suggestions
that led us to investigate alternatives.

The API is unchanged.

While we cannot exhaustively quality-check all possible
sequences across all possible splits (parallelism), it passes
(both DieHarder and TestU01/Crush) those we have checked.

Overall performance with longs and doubles is a little faster,
ints a little slower.

Currently at:
http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/main/java/util/SplittableRandom.java?view=log

-Doug