“White Dog,” a film about a mixed-breed dog who must learn how to survive after a society declares mutts undesirable, won the “Un Certain Regard” prize at the Cannes Film Festival on Friday. Its director, Kornel Mundruczo of Hungary, has said it is an allegory about Europeans’ treatment of minorities. “Party Girl” got an ensemble prize while David Gulpilil was awarded best actor for Rolf de Heer’s “Charlie’s Country.” The competition honors more offbeat films than those up for the Palme d’Or.