title: git diff showing only commits that revision/branch A is ahead of revision/branch B
body: <p>Sometimes I have the following problem:</p>
  
  <ol>
  <li><p>Add some commits in a feature branch.</p></li>
  <li><p>Update master from upstream.</p></li>
  <li><p>Want to see the diff between the feature branch and master, but <code>git diff master</code> shows all of the things that have been added/removed in master, when I really only want to see the commits that the feature branch is ahead of master, not the ones that it's behind.</p></li>
  </ol>
  
  <p>Is there a way to do this without having to merge master into the feature branch?</p>