VATICAN CITY (Reuters) - Pope Benedict slipped out of the Vatican unannounced for the first time in his papacy on Saturday, travelling to the same spot his predecessor did exactly 27 years ago to pray after being elected. The Pontiff visited the shrine to the Virgin Mary at Mentorella, in the mountains about 55 km (34 miles) northeast of Vatican City, where Pope John Paul II went on Oct. 29, 1978. John Paul had said that travelling to Mentorella, in what was the first the many pilgrimages outside Rome of his pontificate, had helped him to pray. John Paul's trip,...