Enable from_int for Z3, as suggested by F. Besson.
Enable from_int for Z3, as suggested by F. Besson.

ssaavedra/why3,douglas-larocca/why3,jpdeplaix/why3,douglas-larocca/why3,jpdeplaix/why3,jpdeplaix/why3,ssaavedra/why3,douglas-larocca/why3,ssaavedra/why3