NAJAF, Iraq (Reuters) - Iraq's top Shi'ite cleric arrived in Najaf Thursday to try to end a bloody three-week uprising as tensions rose sharply following attacks in a nearby town that killed 45 people and wounded 170. Grand Ayatollah Ali al-Sistani drove into the battered holy city of Najaf in a huge convoy, guarded by dozens of police pickups with their sirens wailing. Scores of police brandished AK-47 rifles as they drove past thousands lining the streets. The violence in nearby Kufa came as Sistani's efforts to try to persuade fighters loyal to rebel cleric Moqtada al-Sadr to leave Najaf's...