In the past there was one with a straight line going from one piece to the next.
Now there are two, going from one piece to the point on the geometry, and the
second going from the point on the geomety to the next piece.
They are now zero-volume.
They fix:
1) crossings of sides with flat-ends (unit-test cases curve, field_sprayer, bend_near_start)
2) joins with limited number of points (unit-test cases concave_b_rough, italy_part, nl_part)
3) joins with large distances
4) many self-intersections on remaining aimes-cases
It now simplifies first and removes second point if necessary. Also it is
defensive such that generation is stopped if length is 0.
Including unit tests.
