Remove code that isn't really used anywhere else.

  - Leave it as part of the test module as that's the only consumer.
Move more of the setup to the base setup.

  - Instead of having it in the doctest file.
Fix the subrepo redirection failure.

  - As repoze no longer used, so no shortcut out of the view by the use
    of redirect exception.
  - Corrected the update/render pattern to avoid calling render if
    redirect is triggered.
  - Also took the liberty to change the overridden __call__ methods to
    just follow the update/render pattern
  - Proper test case harness (and tests for those) added to ensure that
    the subrepo redirection is not accidentally removed/broken in the
    future.

Progress towards: tracker item 3519