Disable clause database simplification when doing model enumeration.

This bug occurs while maximizing an objective function made of a single
literal. In this case, the returned objective values was negated.

In maximization procedures, the values shown in object lines ("o"), were
wrong, due to a wrong correction applied in the minimization subprocess.

This is temporary fix. Must be improved after the CSP competition.

Competition output is made of "c", "s", "o" and "v" lines (just like SAT
competition output). Competition output is enabled when the
"CompetitonOutput" JVM property is set.

Added another kind of "channel" constraint, and a first "circuit"
constraint.