title: django admin redirects to wrong port on save
body: <p>I have a django project set up with nginx+apache. The http port for outside access is 20111 which is then forwarded to the server machine (which has an internal IP) to port 80. So nginx listens on port 80 (and passes relevant requests to apache on port 5000). </p>
  
  <p>Now the initial login can be reached from the outside via <a href="http://externalip:20111" rel="noreferrer">http://externalip:20111</a> - but when I complete an admin action, like saving an entry, I get redirected to <a href="http://externalip/path/to/model" rel="noreferrer">http://externalip/path/to/model</a> -- without the port 20111. The result is a timeout. How can I tell django to use a specific hostname/port (i.e. <a href="http://externalip:20111" rel="noreferrer">http://externalip:20111</a>) for all admin redirects? </p>