Improved Toolhead adapter for RepMan to Thing-O-Matic

THIS IMPROVED ADAPTER IS A WORK IN PROGRESS.
I HOPE TO TEST IT NEXT WEEKEND ON GulaschProgrammierNacht.

Improvement:
* use a third M5 hole that already exists in the Thing-o-Matic to stabilize the adapter against backlash in milling
* grip the edge of the toolhead-platform for added stability

This should allow me to do the PCB milling much faster without loosing precision to backlash.

Blog post:

http://marcuswolschon.blogspot.com/2011/06/improved-repman-to-tom-toolhead-adapter.htm