Registration of custom chat commands and menu-items for protocols was
done by the IM_REGISTER_* messages, and is now done through direct calls
to the CayaProtocol object.
The new model for call/message for protocols is this: Temporary
information (chat messages, roster members, etc.) should be accessed
through messages. Relatively static data (protocol name, commands)
should be accessed through direct calls to the protocol object.
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