title: Extbase addAdditionalHeaderData(...) in actioncontroller, include same CSS twice
body: <p>For my extbase extension I need a CSS that I include in all actioncontrollers with:</p>
  
  <pre><code>$this-&gt;response-&gt;addAdditionalHeaderData('&lt;link rel="stylesheet" type="text/css" href="' . t3lib_extMgm::siteRelPath($this-&gt;request-&gt;getControllerExtensionKey()) . 'Resources/Public/css/mystyle.css" /&gt;');  
  </code></pre>
  
  <p>If I now have a page where multible plugins of my extensions are included, I have multible CSS includes:</p>
  
  <pre><code>&lt;link rel="stylesheet" type="text/css" href="typo3conf/ext/myext/Resources/Public/css/mystyle.css"&gt;
  &lt;link rel="stylesheet" type="text/css" href="typo3conf/ext/myext/Resources/Public/css/mystyle.css"&gt;
  </code></pre>
  
  <h2>Edit</h2>
  
  <p>I could also do the following:</p>
  
  <pre><code>$GLOBALS['TSFE']-&gt;additionalHeaderData[100] = '&lt;link ...&gt;';
  </code></pre>
  
  <p>But as far as I know is that just the old way.</p>