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.
discarded now. This fixes behaviour of assign_parents with positive-rings in positive-rings (when
check_for_orientation is true; normally (for overlay) it is false)
It also reverses a negative-only ring so fixes a linestring_buffer testcase.
For multi-polygon it fixes new testcase rt_u2 found by recursive-polygon-buffer test
This moves responsibility of generation to the calling code, removes it
from the join strategies. It also enables using the end-strategy for the
spikes
