class SplittableRandom

[Doug Lea]

I incorporated updates stemming from yesterday's SplittableRandom
list and off-list traffic. Thanks as always for all the helpfulness.

Mike Duigou: It's probably reasonable to let lambda and webrev
versions lag a few days until a bit more stable. Until then, see

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

-Doug