QPID-5045 - Refactored the router data structures to support message and link routing.
QPID-4997 - Fixed the thread safety problem.

 - Wrapped "pn_delivery" in the container to allow for explicit linkage of delivery pairs.
 - Removed the linkage between "message" and "delivery".  Messages can now be discarded as
   soon as the last copy is delivered because their status will be tracked in the dx_delivery
   object.
 - Removed tx_handler from the set of callbacks in the container.  There is no need for this
   notification (sendable delivery) because Dispatch does not create outbound deliveries
   until it is ready to send them (i.e. deliveries are created and advanced in one synchronous
   operation).
 - Replaced the out_fifo of messages per outbound-link with a pair of fifos (one for messages
   and one for state changes) per link.  Note that even inbound-links need to send state
   changes outbound.  This change addresses QPID-4997.



git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1511021 13f79535-47bb-0310-9956-ffa450edef68