RFR 8181104 Fix specs for updateAndGet and related methods

[Paul Sandoz]

Hi,

http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8181104-updateAndGet-atomicty-ordering/webrev/index.html

This patch fixes two spec issues:

1) j.u.concurrent.atomic.* classes now defer to VarHandles and package doc was removed. This inadvertently removed a clause about the memory order effects of the read-modify-write methods. So the relevant methods were updated.

2) The VarHandles CAS specification slightly changed the semantics of memory ordering effects when the CAS fails. A general paragraph was added specifying the effects of plain, opaque, acquire/release, and volatile operations.

Thanks,
Paul.