The latest Twisted fixes the web.Agent code we need for proper async
support. There's still a daemonization bug that prevents 'wormhole
server start' from succeeding (it hangs).
The "bytes % bytes" syntax only appeared on py3.5, so don't use it.
Updated travis to expect py3.4 works.
The twisted side is probably even more broken for py3.4 than it is for
py3.5.