Officials Play Down Plan Described in Secret FBI BulletinDirt roads trace pale lines across a desolate landscape of bald peaks and plunging canyons near Texas' Big Bend and bridge the border at dozens of improvised crossings. For decades, these routes have been used to smuggle drugs and humans. Now there is growing concern they could become deadly conduits for terrorism. The concern is buttressed by a confidential but unclassified FBI intelligence bulletin * * * The plot, according to uncorroborated information provided by an FBI informant, involves a man, described as an Arab who goes by the nickname "El Español,"...