title: responseXML is null
body: <pre><code>url = "http://localhost/xml.php?type=xml";
  if (window.XMLHttpRequest) {
        xmlhttp = new XMLHttpRequest();
        xmlhttp.open("GET", url, true);
        xmlhttp.setRequestHeader('Content-Type', 'application/xml');
        xmlhttp.send(null);
  }
  else if (window.ActiveXObject)  {
      xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
      if (xmlhttp) {
          xmlhttp.open("GET", url, true);
          xmlhttp.setRequestHeader('Content-Type', 'application/xml');
          xmlhttp.send();
      }
  }
  
  alert(xmlhttp.responseXML); //returns null
  </code></pre>
  
  <p>XML file</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8" ?&gt;
  &lt;main&gt;
      &lt;food&gt;
          &lt;type&gt;6&lt;/type&gt;
          &lt;region&gt;5676&lt;/region&gt;
      &lt;/food&gt;
      &lt;food&gt;
          &lt;type&gt;6&lt;/type&gt;
          &lt;region&gt;5676&lt;/region&gt;
      &lt;/food&gt;
  
  &lt;/main&gt;
  </code></pre>
  
  <p>Anyone has idea why <code>xmlhttp.responseXML</code> is returning as null?</p>