title: Undoing a merge done with --no-ff
body: <p>I've heard that a <strong>git merge</strong> done with the --no-ff flag preserves full history <em>making it easier to pull out a specific merge</em>. I've not seen it explained, though, how to undo a merge made with --no-ff. Also, I can't see how it makes it easier to unmerge than a fast-forward merge. Can someone shed some light on this, or point me to some good info on this?</p>
  
  <p>Thanks.</p>