Dual Extrusion with Marlin and Pronterface

As promised in http://www.thingiverse.com/thing:123609 showing my dual extruder in successful operation, here is a version of Marlin to support dual extrusion on a Printrboard. Basically, the hard work was done by Denis Bakin (dob71) https://github.com/dob71/Marlin/tree/m (I refer to this as €œMarlin-M) , but was not merged into the version of Marlin used on the Printrboard ( http://blog.lincomatic.com/?p=537). If you are using Printrboard, you are probably already familiar with Lincomatic