Python Swig bindings do not expose Message properties in the same manner as the pure Python bindings

With the pure Python bindings, message properties can be assigned using:

In [3]: msg.properties
Out[3]: {}

In [4]: msg.properties["foo"] = "bar"

In [5]: msg.properties
Out[5]:

However, in the Swig python bindings this results in the property never being set. This is because the call to properties appears to be calling the underlying C++ code and returning a copy of the properties map:

In [3]: msg.properties
Out[3]: {}

In [4]: msg.properties["foo"] = "bar"

In [5]: msg.properties
Out[5]: {}