ArduCopter now has experimental geo-fencing support, thanks to Andrew Tridgell's superb geo-fencing code for ArduPlane.   If you haven't heard of the geo-fencing features of ArduPlane, you are probably an ArduCopter user! Since December 2011, ArduPlane piltos have had the ability to build a virtual fence around an area and prohibit the aircraft from exit from the fence. The details are in the Ge…