Gov. Arnold Schwarzenegger is seldom upstaged, but it could happen Thursday when one of his chief legislative rivals flies south of the border to hold private meetings with Mexican President Vicente Fox. Assembly Speaker Fabian Núñez said he plans to make the trip -- and miss one of the few legislative sessions remaining this year -- in an attempt to repair relations with California's largest trading partner. Schwarzenegger has been sharply criticized by Mexican media and politicians for supporting private border patrols to curb illegal immigration. ``The tension between the governor and the Mexican government began to boil after his...