Listener: don't upcall to missing Service.__init__
Listener: don't upcall to missing Service.__init__

This is causing errors against an older Twisted (14 and 15, but not 16).
I'm puzzled why this is causing a problem now, when it wasn't before..
maybe some other library has changed? Anyways, this seems correct (since
Service doesn't define __init__), and fixes the problem for the older
twisteds.

warner/foolscap,david415/foolscap