title: Where is IUserEventHandler located in Orchard 1.6?
body: <p>I am attempting to extend the Orchard login process using IUserEventHandler, like is done <a href="https://stackoverflow.com/questions/11585608/orchard-cms-sign-out-log-off-confirmation-page">here</a>.  No matter how hard I look through the Orchard assemblies, I can't find the Orchard.Users.Events namespace which is the supposed home of IUserEventHandler.</p>
  
  <p>Which Orchard assembly contains that interface?</p>