title: attributeRemoved not being called after session.invalidate
body: <p>I have a object that implements the <code>HttpSessionAttributeListener</code>, and as you'd expect it does some work when certain objects are added, replaced and removed from the session.  </p>
  
  <p>I thought that the if the session is ended [<code>session.invalidate()</code>], each object from that session is removed from the session as so the <code>attributeRemoved()</code> method would be called? I'm not seeing that behavour and wondered if I dreamt it. </p>
  
  <p>To ensure I can be notified when the session is invalidated do I have to implement <code>HttpSessionBindingListener</code> on the object i'm interested in? or is there another way. </p>