title: How to prune local tracking branches that do not exist on remote anymore
body: <p>With <code>git remote prune origin</code> I can remove the local branches that are not  on the remote any more.</p>
  
  <p>But I also want to remove local branches that were created from those remote branches (a check if they are unmerged would be nice).</p>
  
  <p>How can I do this?</p>