MEDINA, Saudi Arabia – At the cemetery where the Prophet Muhammad's family is buried, an Iranian Shiite Muslim pilgrim overcome with emotion was jerked by a Saudi soldier, who barked a sharp order: "Stop crying!" The soldier, a gun at his hip, then hovered over the pilgrim as he wrapped up his prayers to make sure he didn't start weeping again. The Baqee cemetery is where the bitter rivalry between Sunni powerhouse Saudi Arabia and Shiite Iran gets personal. Iranians and other Shiites flock to the graves to pay respects to several revered descendants of Islam's prophet, while Saudi soldiers...