whyconf: reuse prover_altern for comparison, equality, hash and pretty-printing
whyconf: reuse prover_altern for comparison, equality, hash and pretty-printing

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