unstable redundant constraints #1723

(huh, issue template missing? anyway...)

bug-parallel-redundant-not-always.slvs.gz

• Mark r00b and r00e as parallel. This is immediately marked as redundant.
• Do the same for the other pair of lines, r00c and r010. No immediate message about redundancy, it only shows when you try to drag any of the points.
  • It also shows when followed by immediate undo-redo cycle.
  • Also, while dragging, c014-eq-length is constantly popping in and out of redundant constraints list.

Reproducible with 3.1~70bde63 and 3.2~27b6a08.