NO-JIRA: Added connection timeout to python client, used in brokertests.

Added an optional timeout parameter to Connection.establish.
Set a timeout of 5 seconds in brokertest.py to prevent hanging tests.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1487578 13f79535-47bb-0310-9956-ffa450edef68
QPID-4886: Pass non-const reference to Message in QueueObserver functions.

Instead of modifying QueueObserver, a new class MessageInterceptor was
introduced to allow messages to be modified.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1487579 13f79535-47bb-0310-9956-ffa450edef68