title: Composite component required="true" not respected
body: <p>In the composite:interface I have defined an attribute like this:</p>
  
  <pre><code>&lt;composite:attribute name="myAttribute" required="true"/&gt;
  </code></pre>
  
  <p>Now when I use my composite component like this, without defining any attributes:</p>
  
  <pre><code>&lt;myTag:myCC/&gt;
  </code></pre>
  
  <p>I would expect an error to occur. It doesn't. What could I possibly be missing?</p>