Review request for 6666739 and 6711667

[Alan Bateman]

6666739: (ref) ReferenceQueue.poll() doesn't scale well
6711667: (ref) Update SoftReference timestamp only if clock advances

This is forward-port from 6u14 of two scalability fixes. These were 
original fixed by Tom Rodriguez in an earlier update.

The webrev is here:
  http://cr.openjdk.java.net/~alanb/6666739%2b6711667/webrev.00/

Thanks,

Alan.