Aug 26th 2011, 7:52 by N.V. | LOS ANGELES LAST week’s bombshell announcement by Hewlett-Packard that it was hiving off its personal-computer business—and, in particular, would cease making tablet computers and mobile phones forthwith—was greeted with shock and horror, plus a 20% plunge in share price. Canny investors promptly snapped up the depressed stock, realising …