if a way is closed, iD needs to choose a second node to
split the way at.
This algorithm looks for a node that is both far away from
the initial node in terms of way segment length and nearby
in terms of beeline-distance. This assures that areas get
split on the most "natural" points (independent of the number
of nodes).
For example: bone-shaped areas get split across their waist-
line, circles across the diameter.
