First attempt at fixing deadlock when stitching. This happens if both
sides try to stitch at the same time. One side has to back off and let the other proceed. The problem is with the slice locking, which had to be changed to allow one side to drop the lock so the other side could proceed. I ended up doing this with an additional stitching lock, used only when stitching.
Showing with 203 additions and 65 deletions