formats, with the proper color and width. This may need a bit of
cleanup for stuff like the hidden line removal, which currently
loses the style.
Also fix a bug in the test for arcs of a circle. A second-order
Bezier with collinear control points really is an arc, but it's an
arc with infinite radius so stuff tends to blow up. So return false
for that one.
[git-p4: depot-paths = "//depot/solvespace/": change = 2030]
