- The pyramid Router attempted to set a value into the key
  ``environ['repoze.bfg.message']`` when it caught a view-related exception
  for backwards compatibility with :mod:`repoze.bfg` during error handling.
  It did this by using code that looked like so::

                    # "why" is an exception object
                    try:
                        msg = why[0]
                    except:
                        msg = ''

                    environ['repoze.bfg.message'] = msg

  Use of the value ``environ['repoze.bfg.message']`` was docs-deprecated in
  Pyramid 1.0.  Our standing policy is to not remove features after a
  deprecation for two full major releases, so this code was originally slated
  to be removed in Pyramid 1.2.  However, computing the
  ``repoze.bfg.message`` value was the source of at least one bug found in
  the wild (https://github.com/Pylons/pyramid/issues/199), and there isn't a
  foolproof way to both preserve backwards compatibility and to fix the bug.
  Therefore, the code which sets the value has been removed in this release.
  Code in exception views which relies on this value's presence in the
  environment should now use the ``exception`` attribute of the request
  (e.g. ``request.exception[0]``) to retrieve the message instead of relying
  on ``request.environ['repoze.bfg.message']``.

Closes #199.