Squirmer VTK output
Follow up to !20 (merged). Since SphereVtkOutput doesn't go through the type system (where the squirmer could automatically have been upcast to the sphere), it needs to explicitly check for types derived from Sphere.
Follow up to !20 (merged). Since SphereVtkOutput doesn't go through the type system (where the squirmer could automatically have been upcast to the sphere), it needs to explicitly check for types derived from Sphere.