hg: jdk9/sandbox/jdk: Add support for a reachability fence.

[paul.sandoz at oracle.com]

Changeset: 433114b32d2d
Author:    psandoz
Date:      2015-10-06 18:42 +0200
URL:       http://hg.openjdk.java.net/jdk9/sandbox/jdk/rev/433114b32d2d

Add support for a reachability fence.
Contributed-by: dl at cs.oswego.edu, aleksey.shipilev at oracle.com, paul.sandoz at oracle.com

! src/java.base/share/classes/java/lang/ref/Reference.java
+ test/java/lang/ref/ReachabilityFence.java