Subscription.emit with backend argument just returns the backend

[jpic]

Currently, SubscriptionManager.emit accepts a backend argument. It would seem that the behaviour would be the same than when no backend is specified, but it is not the case:

16     def emit(self,*args,**kwargs):
17         backend = kwargs.pop('backend',None) or None
18 
19         if backend:                                                                                                                                                 
20             return subscription.get_backends()[backend]
21 
22         for backend_module in subscription.get_backends().values():
23             backend_module(*args,**kwargs)