DrBotIRC: add method to register a function to the XML-RPC server

this appears to be safe to do while the other thread is doing serve_forever()

DrBotIRC.py

@@ -196,6 +196,13 @@ class DrBotIRC(irclib.IRC):
             except Exception as e:
                 print("exception floated up to DrBotIrc: " + str(e))
 
+    def xmlrpc_register_function(self, func, name):
+        """Add a method to the XML-RPC interface."""
+
+        if func:
+            if hasattr(func, '__call__'):
+                self.xmlrpc.register_function(func, name)
+
     def _xmlrpc_listen(self):
         """Begin listening. Hopefully this was called in a new thread."""