This corrects an issue with fill segments-per-circle and moves the error
to segmetns calculation down in a number of functions to expose the
single value for approximation
Allows 0 to 4 chamfered corners, not only one.
A custom shape allow this kind of shape. However because it is a primitive,
it is easier to edit and it support thermal reliefs.
* Specctra exported polygons are now closed (as required)
* export custom shape is provided in code, but not activated, because i have no way to text it
* fix Specctra export dialog (replace OK and Cancel buttons by only one Close button)
Seth Hillbrand
Andrei Pozolotin
jean-pierre charras
Jeff Young