fix a bug of Dispatcher.add_class when using as decorator

Below is the code to reveal this bug:

    @dispatcher.add_class
    class ProcessOrderAPI(APISet):
	rpc_exports = ['query', 'detail', 'start', 'update']
	rpc_method_prefix = 'ProcessOrder'
	Model = ProcessOrder

	def update(self, object, attrs):
	    # NOTE HERE: Since add_class retuns None previously,
	    # So the 1st argument of super() is None
	    return super(ProcessOrderAPI, self).update(object, attrs)

Author: wonderbeyond

jsonrpc/dispatcher.py

@@ -73,6 +73,8 @@ def add_class(self, cls):
             prefix = cls.__name__.lower() + '.'
         self.build_method_map(cls(), prefix)
 
+        return cls  # for working as decorator
+
     def add_object(self, obj):
         prefix = obj.__class__.__name__.lower() + '.'
         self.build_method_map(obj, prefix)