Segment.intersection() needs updating

[Bentleysb]

#373 updated Segment.intersects() to fix a bug where single point intersections would sometimes be mis-computed, due to a precision error. However, it did not update the companion method, Segment.intersection(), that returns the actual intersections. So Segment.intersects() can now return true but Segment.intersection() will return null for the same segments. This can create NullPointerErrors when the methods are used in conjunction.