A young computer whiz from New York City has launched a site to help people buy cheap plane tickets. But an airline company and its travel partner want to shut him down. United Airlines and Orbitz filed a civil lawsuit last month against 22-year-old Aktarer Zaman, who founded the website Skiplagged.com last year. The site helps travelers find cheap flights by using a strategy called “hidden city” ticketing. The idea is that you buy an airline ticket that has a layover at your actual destination. Say you want to fly from New York to San Francisco — you actually book...