title: flex 3.5: how to scroll at the end of the <mx:list>?
body: <p>I use flex3.5 and I have a</p>
  
  <pre><code>&lt;mx:List id="globalchat_txt" x="0" y="0" width="100%" height="100%" variableRowHeight="true"  dataProvider="{messages}" itemRenderer="chat.MessageChat"&gt;
  </code></pre>
  
  <p>I add some items to messages.</p>
  
  <pre><code>    var message:Message = new Message(txt);
  globalchat_txt.validateNow();
  messages.addItem(message);
  globalchat_txt.scrollToIndex(messages.length+1);
  globalchat_txt.verticalScrollPosition = 99999;
  globalchat_txt.validateNow();
  </code></pre>
  
  <p>I cannot make the list scroll to the last position !
  it goes to last position, but there is alsways like 10-15pixels missing !</p>
  
  <p><img src="https://i.stack.imgur.com/noVi0.jpg" alt="enter image description here"></p>