MAIDUGURI, Nigeria — Muslim extremists from the Boko Haram sect shot and killed a Church of Christ in Nigeria (COCIN) pastor and his church secretary June 7 in Maiduguri, in northeastern Nigeria’s Borno state. Pastor David Usman, 45, and church secretary Hamman Andrew are the latest casualties in an upsurge of Islamic militancy that has engulfed northern Nigeria this year.…