The `xmlrpc.XMLRPC` `handle_*` methods don't appear to work like the base web Resource handlers (yay!). They can just return deferreds (that fire with the XML-RPC serializable result, i.e. probably a dictionary with whatever the spec says we should return). This makes our life quite a bit nicer -- we can just do `return self.transport.handle_raw_inbound_message(...)` and have `handle_raw_inbound_message()` return a suitable deferred. The handler with also probably take a rather different set of arguments to those listed currently (i.e. whatever the spec says the XML-RPC call arguments are).