LOS ANGELES (AP) - As part of a crackdown on undocumented workers employed in sites deemed important to national security, immigration officials arrested six men they said were Mexican nationals working for a company that helps build military housing. U.S. Immigration and Customs Enforcement agents apprehended the men as they arrived for work Friday at Fort Irwin, east of Barstow. The agency said the men worked for Laurence-Hovenier, Inc., a Corona-based company that does construction framing for housing at the Army base. The company's Fred Hovenier said his business didn't hire anyone without proper documentation. "If they were working for...