RFR 8162106 Remove VarHandle.addAndGet

[Paul Sandoz]

Hi,

Please review the following webrev which removes VarHandle.addAndGet:

  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8162106-vhs-rm-addAndGet/webrev/ 
<http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8162106-vhs-rm-addAndGet/webrev/>

This turns out to be really just a helper method which is built upon getAndAdd.

I had to update some classes in j.u.concurrent.atomics.

Thanks,
Paul.