The raytracing code has its own version of camera that maintains two
field of view (fov) parameters: one for the x direction and one for the
y. The standard vtkm::rendering::Camera contains only one fov. As is
consistent with OpenGL's gluPerspective and VTK's camera, the fov is
specified in the y direction. However, the raytracing code was
incorrectly using it in the x direction. That caused it to do a weird
rescaling when the aspect ratio was not 1.