HORNETQ-1275 - Deadlock in stomp delivery

The cause of deadlock is that the direct delivery and indirectly delivery happens at the same time during the stomp delivery
By change the stomp session not to use direct delivery will prevent such a dead-lock.
HORNETQ-1276
By stopping the session first we can avoid the deadlock
HORNETQ-1279
Fix NPE. By initiating the availableCredits inside the constructor we can avoid the NPE happening.
Merge pull request #1393 from gaohoward/br_HQ1275_master

HORNETQ-1275, 1276, 1279