title: call dbus method on proxy without blocking (or no timeout)
body: <p>I'm trying to lock my GNOME screensaver, however the dbus <code>.Lock</code> method is waiting for a response. I would like it to <em>not</em> wait for a response (just send the signal to lock the screensaver, and continue on with life). How do I do this? (In practice this code is in a thread so I continue on with life, but I still get the nasty error)</p>
  
  <pre><code>session_bus = dbus.SessionBus()                                                                                                                                       
  screensaver_proxy = session_bus.get_object('org.gnome.ScreenSaver', '/org/gnome/ScreenSaver')                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
  locked = screensaver_proxy.Lock(dbus_interface='org.gnome.ScreenSaver')
  print "HELLO" # will never get called, due to:
  /*
    locked = screensaver_proxy.Lock(dbus_interface='org.gnome.ScreenSaver')
    File "/usr/lib/pymodules/python2.6/dbus/proxies.py", line 68, in __call__
      return self._proxy_method(*args, **keywords)
    File "/usr/lib/pymodules/python2.6/dbus/proxies.py", line 140, in __call__
      **keywords)
    File "/usr/lib/pymodules/python2.6/dbus/connection.py", line 620, in call_blocking
      message, timeout)
    DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken
  */
  </code></pre>