Remove useless method.
Apply FORCE on the order of the model.

It was previously applied on the order given by an unordered_map.
Can set a number of FORCE iterations.
Fix FORCE span computation.
Merge branch 'refs/heads/master' into force-stats
Update exception message.
FORCE: keep the order with smallest span in a number of iterations.
Merge branch 'refs/heads/master' into linear_allocation