QPID-5716: Messaging C++ .NET binding fails to return GetContentObject data
Changes function signature to: object = message.GetContentObject()
Adds self tests using SetContentObject and GetContentObject.


git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1589496 13f79535-47bb-0310-9956-ffa450edef68