title: Twisted.web File directory listing issues
body: <p>I'm trying to use Twisted in a web-app, and I'm coming across an interesting issue. I'm very new to Twisted, so I'm not sure if I'm seeing a bug in Twisted, or if I just am not using it correctly.</p>
  
  <p>Theoretically from the example, a File resource object can be use to both serve files from a directory, as well as provide the directory listing. So assuming I have the variables (port, reportsDir) defined elsewhere before the code snippet, I do the following:</p>
  
  <pre><code>rootResource = Resource()
  rootResource.putChild("reports", File(reportsDir))
  reactor.listenTCP(port, Site(rootResource))
  reactor.run(installSignalHandlers=False)
  </code></pre>
  
  <p>Now, when I access '/reports' on my host I get a message "Request did not return bytes" in my browser with a bunch of stuff that was obviously produced by twisted, but also contains a print of a u'.....' string literal, which in fact has the directory listing in it. So the DirectoryLister is obviously creating the listing HTML, but it isn't seeing as valid by something in Twisted. It doesn't seem to like the unicode string; which was in fact produced by Twisted itself.</p>
  
  <p>Do I need to set some other configuration item to get it to convert the unicode string to the necessary bytes object (or whatever), or some other approach?</p>
  
  <p>Many thanks, </p>
  
  <p>-D</p>