title: pre-fetch hook functionality in git
body: <p>in my scenario i maintain a svn-synchronized git repository on a server.
  all developers in my group use this repository to get their updates.<br>
  i couldn't find a way to trigger an automatic "git svn fetch" (or any other command) <em>before</em> a developer fetches the latest changes.<br>
  my current workaround is to have a cron job that syncs in svn related changes every 5 minutes.
  is it possible to have this kind of a <strong>pre-fetch hook</strong> at all?<br>
  thanks</p>