Crash stuns families 12/22/2002 By SELWYN CRAWFORD and STAISHY BOSTICK SIEM / The Dallas Morning News The words of Cleburne High School principal Justin Marchel seemed haunting Saturday, just one day after he had uttered them to students. "The last thing I told them as they got out for Christmas break was to be careful because we wanted them all to come back next year," said Mr. Marchel, in his first year as principal of the 1,600-student school. Hours later, junior Steven Bivins, 17, was dead and six other teens were injured after a head-on collision at the top...