Transportation stocks have been excelling in 2013 so far, even with crude oil prices refusing to bend lower. Within the sector, airlines have been flying high. IBD's Transport-Airline industry group, ranked No. 14 among 197 industry groups for six-month relative price performance, is up 9.8% since Jan. 1. One of the leaders, Alaska Air Group (ALK), has enjoyed a stellar run since it cleared a three-month saucer base in mid-October at 38.56. That