CANCUN, Mexico (Reuters) - U.S. President George W. Bush reassured Mexican President Vicente Fox on Thursday he was committed to getting the U.S. Congress to approve broad immigration reforms, including a guest worker program. (snip) "I'm committed to having a comprehensive immigration bill on my desk, and by comprehensive I mean not only border security, a bill that has border security, a bill that has security enforcement in it, but a bill that has a worker permit program in it," Bush said. Republicans are split on whether to back Bush's call for sweeping reforms to create a guest worker program...