I had forgotten to skip the refined tests when the sphere was entirely on
the relevant side of the plane. Now BasePortalVis for gmsp3v2 takes 11s on
my machine (it was 13 with the previous optimization and 15.9 before that).
Also, write some comments describing how BasePortalVis works.
Representing the side of the plane on which the sphere lies is much more
useful as more complicated tests can be done using just the one call.
-1: the sphere is entirely on the back side of the plane
0: the sphere is intersecting the plane
1: the sphere is entirely on the front side of the plane
While noticeably slower than the previous expanded set manipulation code,
this is much easier to read. I can worry about optimizing the set code when
I get qfvis behaving better.
