Fix a bug in the segment-to-segment linking part of sparse tracker.

This bug has the same causes than the previous one, and that affected
the frame-to-frame linking. It has of course the same fix.
I just wished I had discovered it before releasing v2.5.2.
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Fix a bug when loading at the tracker configration panel state.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Release v2.5.3

- Fix a bug in the sparse LAP tracker affecting the segment linking
  part.
- Fix a bug when loading at the tracker config state.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Bump to next development cycle.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>