A major U.S. bank has funded its first home loans to undocumented Mexican immigrants in San Diego County in a move that targets a lucrative, wide-open market while providing new grist for the debate over illegal immigration. The local program, which uses tax identification numbers instead of Social Security numbers, is similar to programs run by small lenders – and two state agencies – around the country that have distributed millions of dollars to undocumented immigrants over the past few years. “There is a huge untapped market out there, but it is a controversial program,” said Sarah Lumbert, office director...