Added:
- A2_USER_FILTER and A2_USER_EXCLUDE settings, contains kwargs for
User.filter() and User.exclude(),
- two helper methods for backends: authentic2.backend.get_user_queryset() and
authentic2.backend.is_user_authenticable(),
- all backends modified to use those.
It should contain the slug of the service from which the user was coming before
requiring login or registration. It's passed to the 'login' and 'registration'
event hooks.
It should limit the possibity of duplicate accounts BUT as the email field is
not really unique at the database level, we cannot really garantee it.
To improve on the current state we should dynamically create unique constraints
on the mail field based on OU.email_is_unique or A2_EMAIL_IS_UNIQUE parameters.
That's not in the current scope.