- Pyramid now expects Response objects to have a __call__
  method which implements the WSGI application interface
  instead of the three webob attrs status, headerlist
  and app_iter.  Backwards compatibility exists for
  code which returns response objects that do not
  have a __call__.

- pyramid.response.Response is no longer an exception
  (and therefore cannot be raised in order to generate
  a response).

- Changed my mind about moving stuff from pyramid.httpexceptions
  to pyramid.response.  The stuff I moved over has been moved
  back to pyramid.httpexceptions.