Commercial Demand and Europeans Drive PC Sales By MARK JEWELL    BOSTON (AP) -- Worldwide shipments of personal computers grew nearly 12 percent in the third quarter, driven by strong European sales and rising commercial demand, according to IDC, a research company that tracks shipments.    A PC shipments report released Monday by another firm, Gartner, Inc., reported quarterly growth of 9.7 percent, with lower-than-expected U.S...