we're inconsistent (singular Jacobian). That's slow, so we should
provide a library interface to disable it.
[git-p4: depot-paths = "//depot/solvespace/": change = 1946]
little test app that links against it. I still need to polish a few
things, but this is more or less as it should be.
[git-p4: depot-paths = "//depot/solvespace/": change = 1944]
Jonathan Westhues