Before this commit, parallel constraints in 3d are fragile:
constraints that are geometrically fine can end up singular anyway
because VectorsParallel() pivots wrong but converges anyway.
After this commit, much like in cc07058, the constraints are written
in a different form: instead of trying to remove two degrees of
freedom out of three, all three are removed, and one added; namely,
the constraint introduces a free parameter, signed length ratio.
This is a bit slow, but more importantly creates a race condition
where e.g. a failing "normal" test will be overwritten by
a succeeding "normal_migrate_from_v20".
This shouldn't ever be a problem since saving dumps the entire
internal state, or is supposed to, at least.
The check was actually half-broken from the beginning and
until df83ee4; the thick red line was rendered properly but
the error text was rendered with width 0, which by chance worked
on some GL implementations. That commit has fixed the underlying
bug but left the text line width at 0 to avoid test breakage.
This commit fixes the bug, turns off the check completely, and
updates the tests to account for breakage.
whitequark
EvilSpirit