add a different exit code on unproved
This is a simple fix for #309 (closed). On unproved goals, we just exit with 2 instead of one.
Prochaines maintenances programmées: lundi 06/05, lundi 03/06, lundi 01/07
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This is a simple fix for #309 (closed). On unproved goals, we just exit with 2 instead of one.