MEXICO CITY (Reuters) - Mexican President Vicente Fox called recent U.S. measures to stem illegal immigration a step back for bilateral relations on Friday and said Mexican migrants do jobs "that not even blacks want to do." In comments likely to raise the temperature of the immigration debate, Fox defended the role of undocumented Mexican workers in the United States to a group of Texas business people meeting in Mexico. "There is no doubt that Mexicans, filled with dignity, willingness and ability to work are doing jobs that not even blacks want to do there in the United States," he...