Specialty-apparel retailers enjoyed a pick-up in sales over the extended holiday weekend that began on Thursday as colder weather unleashed pent-up demand for winter clothing, Sarah Quinlan, a senior vice president at MasterCard, said in a sneak preview of an upcoming spending report by the company. Department stores, however, did not enjoy a similar boost, reflecting the segment’s ongoing struggles to attract consumers, Quinlan said. “All year long, department stores have remained very very challenged.