better error messages for theories/modules not found in loadpath
better error messages for theories/modules not found in loadpath

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