RFR 7117360: Warnings in java.util.concurrent.atomic package

[Chris Hegarty]

Cleanup compiler warnings in the java.util.concurrent.atomic package.

This is a sync up with the raw type warning fixes in Doug's CVS, along 
with some minor style cleanup.

With this change there are still 2 outstanding unchecked casts in 
AtomicReferenceArray and AtomicReferenceFieldUpdater. Will contact Doug 
separately about suppressing these.

http://cr.openjdk.java.net/~chegar/7117360/webrev/

-Chris.

P.S. I have already review this, and the contribution is of course from 
Doug.