AT least 50 people were killed and dozens abducted by gunmen in Nigeria's Plateau state, residents and a community leader said, the latest in a spate of attacks by armed gangs in northern parts of Africa's most populous nation. Such attacks are not common in Plateau, in central Nigeria. But the state shares a border with Kaduna state, where suspected bandits - a loose term for gangs of outlaws carrying out robberies and kidnappings - blew up train tracks, killed eight people and kidnapped dozens last month. Fifteen soldiers were killed last week by gunmen who attacked a Kaduna army…