Interior regions on Edge.Cuts are out as keepouts for specctra DSN file
and downstream routers.  Point to point matching during polygon assembly
can have individual thresholds, one for board edge and another for interior polygons.
This is more forgiving for sloppy graphical mousers, or those that work without
grid snap on.  Currently the threshold for board edge is at zero, meaning the
board edge has to be precisely defined as a polygon, just as before.  But it
is easily tunable for experimentation.