segments in Boolean against the shell, not the intersection
polygon. (We just cast a ray, and use the surface-line intersection
function that already existed.) That's slow, but can be
accelerated later.
[git-p4: depot-paths = "//depot/solvespace/": change = 1911]
non-coincident faces. There's also a problem when I don't generate
the full intersection polygon of shell B against a given surface in
shell A; I need to modify the code to not require that.
[git-p4: depot-paths = "//depot/solvespace/": change = 1910]