title: `react.cloneElement` ignores className, how can I give something a className?
body: <p>Reading through the docs, it seems that the now deprecated <code>cloneWithProps</code> merged the <code>className</code>s, but <code>cloneElement</code> ignores the <code>className</code> that's passed in</p>
  
  <p><a href="https://jsfiddle.net/z12hc5er/1/" rel="nofollow">https://jsfiddle.net/z12hc5er/1/</a></p>
  
  <pre><code>var Foo = function () {
      return &lt;div className="shows-up"&gt;Hello World&lt;/div&gt;;
  };
  
  var Bar = function () {
      return React.cloneElement(&lt;Foo/&gt;, {className: 'ignored'});
  };
  
  ReactDOM.render(
      &lt;Bar/&gt;,
      document.getElementById('container')
  );
  </code></pre>
  
  <p>Is there any way to influence the className of a cloned element?</p>