Add free function for sudo Python module.

This reduces the amount of memory leaked on unload.

plugins/python/sudo_python_module.h

@@ -29,6 +29,7 @@ extern PyObject *sudo_exc_PluginReject;  // a reject with message
 extern PyObject *sudo_exc_PluginError;   // an error with message
 
 extern PyTypeObject *sudo_type_Plugin;
+extern PyTypeObject *sudo_type_ConvMessage;
 
 PyObject *sudo_module_create_class(const char *class_name, PyMethodDef *class_methods,
                                    PyObject *base_class);