title: Reference current branch and origin/<current> in git alias
body: <p>As an example assume you want to write a git alias, which shows the difference between the current branch and its <code>origin</code> partner.</p>
  
  <p>In the specific case of master it would look like the following:</p>
  
  <pre><code>[alias]
      top = log --oneline --graph --decorate master ^origin/master
  </code></pre>
  
  <p>How to replace <code>master</code>?</p>