RFR(S): 7099824: G1: we should take the pending list lock before doing the remark pause

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers review these changes? The webrev can 
be found at: http://cr.openjdk.java.net/~johnc/7099824/wevrev.0/

Summary: During a G1 remark pause, the JVM may enqueue some discovered 
references on to the pending list. Whenever the JVM modifies the pending 
list, it is supposed to synchronize with the ReferenceHandler thread and 
acquire the pending list lock but G1's concurrent GC operations were not 
doing so.

Testing: the GC test suite with both CMS and G1, and jprt.

Thanks,

JohnC