Keep tangency support in Modify 3D commands

The following tangential transitions are supported with the Keep Tangency option in Modify 3D commands:

	Plane	Cylinder	Cone	Sphere	Torus	Bspline
Plane	n/a	yes	yes	n/a	yes	no
Cylinder	yes	linear: yes circular: no	yes	no	no	no
Cone	yes	yes	yes	yes	yes	no
Sphere	n/a	no	yes	no	no	no
Torus	yes	no	yes	no	no	no
Swept bspline	yes	linear: yes circular: no	yes	no	no	yes
Bspline	no	no	no	no	no	no