title: How to quit a pygtk application after last window is closed/destroyed
body: <p>Is there a way I can tell gtk to automatically call <code>gtk.main_quit()</code> when the last open window of the application is closed/destroyed?</p>
  
  <p>If there is no direct feature offering this functionality, I could think of the following:
  In the window's destroy method: get a list of open windows in the process, if its empty quit. Is there a way to get such a list?</p>
  
  <p>The obvious solution would be to keep manually track of all open windows, but I would want to avoid this if possible.</p>