"History has not been kind to Jefferson Davis." So writes James McPherson in the opening line of "Embattled Rebel: Jefferson Davis as Commander in Chief" (Penguin, 320 pp., $32.95). Indeed, McPherson, eminent Civil War historian and author of the magisterial, Pulitzer Prize-winning "Battle Cry of Freedom," doesn't really care much for Davis either, noting that he "could be austere, humorless, and tediously argumentative."