Sketcher Create3PointArc

Description
This tool draws an arc by picking three points: the start point, the end point and a point on the arc.

Usage
When starting the tool, the mouse pointer changes to a white cross with a red arc icon. The coordinates of the pointer are shown beside it in blue in real time.
 * Pick points on an empty area of the 3D view, or on an existing object (auto constraints must be active in the Task panel).
 * Pressing or clicking the right mouse button cancels the function.