DALLAS - Say goodbye to the Southwest Airlines "cattle call." The Dallas-based airline says it is making changes to its longtime open seating policy to assign a specific pecking order to travelers waiting to board their Boeing 737 jets. Starting in early November, customers of Southwest Airlines Co. will be assigned a letter-number combination on their boarding passes, which will reserve their spot in their boarding group. According to a Southwest statement, when a gate agent calls a boarding group, passengers will take their place in their numerical order. Southwest has tested the new boarding system since last month at...