Cannes-premiering “Kidnapped” offers the comforting pleasures of a cracking tale well told, a handsome tour of Old World locales and a throwback mix of Big Themes served on heaping platters.The story certainly lends itself to such heft, as it follows the true tale of Edgardo Mortara, a Jewish boy confiscated from his family by the all-powerful church and raised to be a priest. What pushed the local authorities to turn up unannounced one night — making demands of a Jewish family that would echo persecutions past and to come – becomes clear when church police set their sight on a 6-year-old boy and tell his parents, “Someone betrayed you.