Add new tags for reference sphere/spheroid concepts.
Add cs::model::sphere<> and cs::model::spheroid<>.
Add get_radius(), set_radius() and radius_type<> functions/metafunctions.
Add tests.
Refactor [extensions] nsphere to use the official functions.
-> added many testcases
Various updates in testcases for support of open polygons
recursive_boxes.cpp, added triangles as well (dropped corner)
[SVN r66450]