[rset] New method: ResultSet.one() This method will return exactly one entity while enforcing its existence and unicity. The idea is shamelessly borowed from SQLAlchemy Query.one(). Closes #3352314 [jcr: use len(self) instead of len(self.rows)]

#!/usr/bin/env python
from cubicweb.cwctl import run
import sys
run(sys.argv[1:])