Shows the use of the serializer hooks to be able to transfer custom classes via Pyro.
If you don't use the serializer hooks, the code will crash with a
SerializeError: unsupported serialized class, but now, it will happily
transfer your object using the custom serialization hooks.

It is recommended to avoid using these hooks if possible, there's a security risk
to create arbitrary objects from serialized data that is received from untrusted sources.
