Fix SWIG wrappers that return BoundingBoxKD.

Closes #843.
Fix intersection of BoundingBoxKDs.
Test ParabolicFit.get_fit_error().
Check get_sphere_patch_3d_geometry().
Check get_transformed() for a BoundingBox3D.
Check Triangle3D.show().
Check get_orthogonal_vector().
Test VectorD<D> operators for unusual D.
Mark slower test as such.
Mark slow test as such.