title: Autobahn websocket issue while running with twistd using tac file
body: <p>I have a WebSocket server implemented using <a href="http://autobahn.ws/" rel="nofollow">autobahn</a> WebSocket framework using twisted. WebSocket server runs fine when the program ran with python. But if I run this using twistd server runner by creating tac file as twisted service, I get the following error in server while any client try to establish connection and the handshake is failing.</p>
  
  <p><code>2015-12-08 07:17:56,022 - CRITICAL - twisted.publishToNewObserver() 154 Unhandled Error
  Traceback (most recent call last):
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/python/log.py", line 84, in callWithContext
      return context.call({ILogContext: newCtx}, func, *args, **kw)
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/python/context.py", line 118, in callWithContext
      return self.currentContext().callWithContext(ctx, func, *args, **kw)
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/python/context.py", line 81, in callWithContext
      return func(*args,**kw)
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/internet/posixbase.py", line 597, in _doReadOrWrite
      why = selectable.doRead()
  --- &lt;exception caught here&gt; ---
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/internet/tcp.py", line 1067, in doRead
      protocol = self.factory.buildProtocol(self._buildAddr(addr))
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/twisted/internet/protocol.py", line 135, in buildProtocol
      p = self.protocol()
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/autobahn/websocket/protocol.py", line 665, in __init__
      self.is_closed = txaio.create_future()
    File "/opt/nrgi-ws/nrgi-ws-virtual-env/local/lib/python2.7/site-packages/txaio/_unframework.py", line 43, in _throw_usage_error
      "To use txaio, you must first select a framework "
  exceptions.RuntimeError: To use txaio, you must first select a framework with .use_twisted() or .use_txaio()</code></p>