title: Undoing a branch merge
body: <p>I just did <code>git pull origin branch</code> accidentally and now I have all these changes merged into <code>master</code></p>
  
  <p>I tried reverting the commit w/ github for mac and got this error:</p>
  
  <pre><code>fatal: Commit d0fbfb0f7d3ea8.. is a merge but no -m option was given.
  </code></pre>