title: after_filter for exceptions
body: <p>Is there something similar to an after_filter that still runs if the action raises an exception?</p>
  
  <p>I'm using an external logger (since I'm on Heroku); the response headers are filtered and logged in the after_filter.  If an exception is raised, the filter doesn't run, and I don't have a log of the response header data.</p>
  
  <p>If I try to hook into log_error or rescue_action_in_public, the response header won't be complete (since the actual render is called after these).  </p>
  
  <p>Is there another function that I can override that will be called at the equivalent time to an after_filter, but always run regardless of whether an exception is thrown?</p>
  
  <p>Thanks!</p>