Bugfix (aka accidentally a tuple):

    * MediaCling debug_cling attribute was not overridden properly.  Was still
      using the staticfiles handler.
    * _transpose_environ treated base_url as a string when it was a tuple.
      By accident, len('/static/') - 1 == len(base_url) + 1 == 7. Breaks for a
      url of any other length.