title: Is there a boost::weak_intrusive_pointer?
body: <p>For legacy reasons I need to use intrusive pointers, as I need the ability to convert raw pointers to smart pointers.</p>
  
  <p>However I noticed there is no weak intrusive pointer for boost. I did find a talk about it on the boost thread list, however nothing concrete.</p>
  
  <p>Does anyone know of a thread safe implementation of weak intrusive pointer?</p>
  
  <p>Thanks
  Rich</p>