QPID-6107: Python Swig wrapped bindings consistently fail with spout and drain

Problem was a missing Py_INCREF in cpp/include/qpid/swig_python_typemaps.i

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1626887 13f79535-47bb-0310-9956-ffa450edef68