qpid::messaging::ConnectionContext crash after network disconnect (with patch)

When doing HA testing we found that our application often crashed inside the Qpid Messaging library.

Our test:

• One ActiveMQ broker.
• Two proxies connecting to the AMQP port on the broker. At the start, only one of the proxies are running.
• Test program configured to use failover between the two proxies. Protocol is "amqp1.0". It reads messages in a loop using a transactional session. On error it closes the connection and opens a new.
• Three queues are read from in parallel, each reader using its own connection in a thread. Nothing is shared between the threads in the client code.
• Send some messages and let the test program process them.
• Stop proxy1 and start proxy2.
• Send some more messages and let the test program process them.
• Stop proxy2 and start proxy1.
• And so on...

After a couple of switches the test program crashes, but not always. It's a timing thing.
A typical error message that we see before the crash:

Exception when trying to close the qpid connection: Transaction outcome unknown: transport failure

The reason for the crash is that the poller thread is still active when the connection is being deleted. The destructor of the qpid::messaging::ConnectionContext class deletes the TcpTransport instance at the same time as, or right before, the poller thread is calling a callback on it (qpid::messaging::amqp::TcpTransport::disconnected).

I have attached a patch to solve the issue, at least for this use case.

I cannot test this on 1.37.0 as I cannot build that version on RHEL6 as it uses Python 2.6 which is no longer supported in 1.37.0. The code in question is identical in 1.36.0 and 1.37.0 though.