Ten years on, it has never landed in the generated docs.

- As with the previous commit, we want to avoid trusting user-supplied data
  from the query string or form parameters when constructing redirect URLs.

- Storing the route name and matchdict for the view being forbidden in
  the session allows us to construct the redirect URL on successful
  login cleanly.

- In order to clarify that the logic of storing the 'came from'
  information is separate from rendering or processing the login form,
  this PR splits the `@forbidden_view` mapping onto a separate view function.

- The narrative doesn't discuss this (mis-)feature.

- Without any authorization, there is no meaninful reason to remember
  the 'previous' page.

- As a general rule, we want to avoid trusting user-supplied data (i.e.,
  from the query string or form params) when constructing redirect URLs.

update SQLAlchemy logger in quick tutorial fixes #3706