Use a specific comparator for the dual objective vector

Because we want to have a separated comparator to use in the archive or…
Use the fitness type instead of the objective vectors in fitness assignments
Replace a cout msg by a eo::log warning
BUGFIX pop split everywhere in exp dual fitness assignment

Apply the fitness assignment on both splited pop, not just one.
Apply also the partial update on splited pop.
Confine numeric valuesto double limits, to avoid overflows.