title: GitHub: Reopening a merged pull request
body: <ul>
  <li>I made some changes</li>
  <li>I submitted a pull request</li>
  <li>The pull request was accepted and merged.</li>
  <li>We found a bug</li>
  <li>The changes were removed again (force push to 1 commit before) whilst I fixed the bug.</li>
  </ul>
  <p>I've now fixed the bug and want to resubmit the pull request with 1 extra commit. Is there any way to reopen the pull request or update it, or do I have to create a new pull request, type out the description etc again? Gitorious has this feature and we've recently moved to GitHub.</p>