.Lo and Beyonce can take another bow. The booty-shaking stars have shaped the newest generation of mannequins, with hundreds of well-rounded plastic backsides appearing in shop windows across New York. Bootylicious figures clad in tight low-rise jeans have spilled from the city's street fashion stores into more established labels. "It's absolutely the trend," said Dwight Critchfield, creative director for mannequin firm Goldsmith. "These mannequins look great, and there is a real sex appeal about them." The recent pop culture fixation on large bottoms has been around since at least 1992, when rapper Sir Mix-a-Lot scored a hit with "Baby Got...