MEXICO CITY -- Mexico's government is warning its citizens about travel to Arizona because of a tough new immigration law there. The travel alert from the Foreign Relations Department urges Mexicans in Arizona to "act with prudence and respect the framework of local laws." It says that the law's passage shows "an adverse political atmosphere for migrant communities and for all Mexican visitors." It says that once the law takes effect, foreigners can be detained if they fail to carry immigration documents. While enforcement details are not yet clear, the alert says "it should be assumed that any Mexican citizen...