so now we've got the exact curve loops, with their direction
standardized so that we can tell which direction is out. We still
need the polygon in any case, since that's a convenient way to find
each curve's winding number.
And remove some more leftover code from mesh sweeps.
[git-p4: depot-paths = "//depot/solvespace/": change = 1897]
piecwise linear segments. These are piecewise linear approximated
for display, and currently for the mesh too, but that's the first
step to replace the mesh with exact curved surfaces.
[git-p4: depot-paths = "//depot/solvespace/": change = 1895]
