title: Add a class attribute with theme_item_list
body: <p>I am trying to create a list with theme_item_list within a hook_block_view function.</p>
  
  <pre><code>$items = array();
  $items[] = array('data' =&gt; l('Training', 'training'));
  $items[] = array('data' =&gt; l('Publications', 'publications'));
  $items[] = array('data' =&gt; l('Conferences', 'conferences'));
  $items[] = array('data' =&gt; l('Information service', 'information-service'));
  $block['content'] = theme('item_list', array('items' =&gt; $items), NULL, 'ul', array('id' =&gt; 'contact-us'));
  </code></pre>
  
  <p>I want the output to be:</p>
  
  <pre><code>&lt;ul id='contact-us'&gt;
      &lt;li&gt;&lt;a href='/training&gt;Training&lt;/a&gt;&lt;/li&gt;
      ...
  </code></pre>
  
  <p>but the class is missing when the output is returned:</p>
  
  <pre><code>&lt;ul&gt;
      &lt;li&gt;&lt;a href='/training&gt;Training&lt;/a&gt;&lt;/li&gt;
      ...
  </code></pre>
  
  <p>I think I've followed the example on drupal.org accurately, but it's not working? Thanks.</p>