-- Mexican authorities are incensed at what they see as racist overtones in California's recently passed Proposition 187, which cuts off state benefits to illegal aliens. In fact, they're encouraging an unofficial boycott of Golden State products. Some trade experts expect a 25% drop in imports from California in the fourth quarter of 1994. That's further bad news for a shrinking U.S. trade surplus with Mexico. It was $5 billion in 1992 and will likely fall to $2 billion this year.