Old versions of Django defined User.is_authenticated() and

User.is_anonymous() as methods, but in modern versions they're

properties. Method usage was deprecated in Django 1.10, but still worked

until Django 2.0.
We're now using the property form for these checks. This is compatible

with all supported versions of Django targeted for Djblets 3.0.

Unit tests pass on Django 1.11 and on 3.2 (when combined with other

in-progress changes).