Implements AMQ-4526: ActiveMQ should automatically restart if a Locker looses it's lock.

* Adds a new broker config option 'restartAllowed'.  Set it to false to revert to the preserve behavior.
* Adds a new 'restart' JMX operation on the broker
* The default IO exception handler will trigger a broker restart instead of a broker stop.

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@1480325 13f79535-47bb-0310-9956-ffa450edef68