update the method to transform to CNF
update the method to transform to CNF

We reduce the number of generated clauses (especially in the case of disjunctions).
We went from exponential to linear in term of the number of clauses in the generated formula.
See http://en.wikipedia.org/wiki/Conjunctive_normal_form.

FredMaris/touist,touist/touist,FredMaris/touist,olzd/touist,FredMaris/touist,olzd/touist,touist/touist,touist/touist,olzd/touist,touist/touist