*** Submitted as
https://code.google.com/p/go/source/detail?r=477b2e70b12d ***
math/rand: add example / regression test
This makes sure the outputs do not change for a fixed seed.
See also https://codereview.appspot.com/6905049.
R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/6907048
https://codereview.appspot.com/6907048/
