Deleted accounts are not handled gracefully

[ThrawnCA]

If an account is deleted, but not entirely purged from the database, then single sign-on will fail without giving an appropriate error message.

The user is sent to the dashboard URL, but not actually logged in (because their account is not active), resulting in a 404 Unauthorized error, without any explanation of the reason.

[duttonw]

Default auth auto logs the user out if not active.
https://github.com/ckan/ckan/blob/master/ckan/views/__init__.py#L105