8005697: Add StampedLock - JEP 155

[Chris Hegarty]

As part of JEP 155 (Concurrency Updates) we are proposing to add 
StampedLock. A capability-based lock with three modes for controlling 
read/write access.

Javadoc:
 
http://cr.openjdk.java.net/~chegar/8005697/ver.00/javadoc/StampedLock.html 
  (some external links are not working in this online version)

Webrev:
   http://cr.openjdk.java.net/~chegar/8005697/ver.00/webrev/webrev/

StampedLock, as usual, is coming from Doug Lea, with assistance from 
members of the former JCP JSR-166 Expert Group. Aleksey Shipilev, Dave 
Dice, and I, have all informally reviewed this, and our feedback is 
already incorporated in this version. This is an official call for 
review before finalizing the API for inclusion in jdk8.

Thanks,
-Chris.