An African Affair by Nina Darnton Viking, $25.99, 256 pages, ISBN 978-0-670-02288-5 Okay, class, raise your hand if you know where Nigeria is located.  If you said “Africa, of course,” you’re right of course, but that’s like saying “the Catskills are in North America.”  It covers a wide patch of territory.  The truth is, I had to go look it up.  Nigeria is in the “dog leg” of the