Consistent circle transform.

Depending on compilation flags, applying a transform used to either:
- work;
- fail throwing an abstract method not implemented message;
- fail silently.

Now it should consistently work, like the other geometries.

Fix #2680 
The way we formutate this we really give the impression that Circle is
special and obey special rules.

I want to clarify this point, maybe there is a better formulation?