Cropping curvy roads on boundaries

[tedsteiner]

Minor bug. When a road leaves the map boundary and later returns, the cropper does not properly handle this. I think that currently the cropper places the road as following the boundary until it re-enters. This will be ok for route planning in some cases (minor curvy roads) but bad for others (such as a long beltline highway).

This should be changed so that these highways are broken up into multiple, shorter ways that lie entirely within the bounds.