Mathematical and Computer Sciences and Engineering Division, 4700 King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia, xin.gao@kaust.edu.sa. Jianhua Z. Huang, Department of Statistics, 447 Blocker Building, Texas A&M University, 3143 TAMU, College Station, TX 77843-3143 (USA), E-mail: jianhua@stat.tamu.edu.