Trapezoid Screw Thread Module: Extrude-Transform Polygons

JelleAtProtospace pointed out that trapezoid screw thread are useful as well, e.g. to make a drivenut for the leadscrew threaded rods used in many CNC machines.

http://en.wikipedia.org/wiki/Trapezoidal_thread_forms

That sounded like a valuable and fairly simple modification, but I wasn't looking forward to modifying the polyhedron command at the heart of the module (adding each new vertex means adding several triangles and making sure they have the right winding order), but like anything e