only those paths, i.e. and not 'x.y.x'; eagerload('children.children')
applies only to exactly two-levels deep, etc. [ticket:777]
+ - PickleType will compare using `==` when set up with mutable=False,
+ and not the `is` operator. To use `is` or any other comparator, send
+ in a custom comparison function using PickleType(comparator=my_custom_comparator).
- query doesn't throw an error if you use distinct() and an order_by()
containing UnaryExpressions (or other) together [ticket:848]