title: How to get only git revisions that are branch heads?
body: <p>Given a history such as</p>
  
  <pre><code>commit         | ref
  ---------------+------------------------------
  3ad2c1         | master
  b34b14         |
  afeg41         | origin/merge-requests/421
  1fea34         |
  6422bc         |
  15fcda         | origin/merge-requests/152
  </code></pre>
  
  <p>How can I can get a list of only the named refs, i.e. <code>master, origin/merge-requests/{421,152}</code> between two given commits?</p>