Autoactivate Shibboleth users

This causes Shibboleth users to be automatically activated.

Unfortunately the doctests currently always pass, even if it they're broken. Thus: I haven't tested that yet.
Then setting the email activation wouldn't be omitted here. However, it would still not be set in `model.User._set_email`, because `email==self._email`. I won't fix that yet, because the semantic on what should happen activation-code wise with shibboleth users without email addresses isn't defined anyway.