KANO, Nigeria (Reuters) - Two Nigerian policeman were killed on Monday at a checkpoint in northern Kano state by suspected militants from the Islamist sect Boko Haram, the government said. After a surge in violence around the turn of the year, there have been fewer attacks by the Islamist militants, although they remain the biggest security threat to Africa's top oil producer. Captain Ikedichi Iwewha, spokesman for joint military and police forces in Kano, confirmed the checkpoint attack and said two civilians who were praying by the roadside were wounded. ...