fixed str2singleton bug in fts.atomic_propositions.label_state so that if a single string s is passed as the state label, then it is replaced by the singleton {s}, before further processing.
fixed str2singleton bug in fts.atomic_propositions.label_state
so that if a single string s is passed as the state label,
then it is replaced by the singleton {s}, before further processing.

tulip-control/tulip-control,tulip-control/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,necozay/tulip-control