[1.5.x] Clarified meaning of models.User.is_authenticated()
[1.5.x] Clarified meaning of models.User.is_authenticated()

Backport of f96fe3cd1e from master

imtapps/django-imt-fork,bliti/django-nonrel-1.5,imtapps/django-imt-fork,hasadna/django,ccn-2m/django,hasadna/django,imtapps/django-imt-fork,hasadna/django,ccn-2m/django,ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django,bliti/django-nonrel-1.5