Macro to generate a sphere_sweep-like object as a mesh2 object, to allow uv
mapping along a spline. Mesh object is uncapped and hollow, no good for
CSG but will do nicely for hoses/wires/ropes etc. as long as you can't see
the ends.
Also includes 'drawspline' and 'helicoil' macros, built up from
cylinder/sphere objects.
