MAIDUGURI, Nigeria, May 6 (Xinhua) -- Abducted former Nigeria's minister of Petroleum, Shettima Ali Monguno, has been released by his abductor Boko Haram in northeast Borno State, a competent security source told Xinhua on Monday.The source told Xinhua on phone that the elder statesman was released in an undisclosed location, three days after he was seized by four gunmen...