JUBA, South Sudan (AP) — A South Sudanese prophet — as the story goes — wielded a sacred stick during a tribal battle in 1878 and summoned a deadly thunderbolt that struck down rival fighters. That stick is known as Ngundeng Bong’s dang, and not only has its reputation as a magical and dangerous weapon lived on, but it also plays a role in the latest cycle of violence in the world’s youngest nation. The dang has emerged as a contentious relic in the quarrel between South Sudan President Salva