Shapes: added missing test for Shape::collides().

There is one not-yet-sure-about behavior, expecting the failure.
Shapes: added Shape::collision().

Much like Shape::collides() is equivalent to the more low-level
collision detection using operator%, the Shape::collision() returns
collision details similarly to operator/. Currently only Sphere/Sphere
and Sphere/Point collision is done, thus the dispatch is nearly empty.
Shapes: removed unused variable from the test.

The purpose wasn't commented at all, so I may just assume that it got
lost after some refactoring.