NEW YORK (Reuters) - Texas oilman David Chalmers and two companies he owns pleaded guilty on Friday to paying millions of dollars in secret kickbacks to Iraq in connection with the United Nations oil-for-food program. Chalmers, 53, pleaded guilty in Manhattan federal court to one count of conspiracy to commit wire fraud, just weeks before he was due to go on trial with Texas oil tycoon Oscar Wyatt. Earlier on Friday, Ludmil Dionissiev, a Bulgarian oil trader based in Houston, pleaded guilty to smuggling. Prosecutors said Dionissiev, 61, worked with Chalmers to buy Iraqi oil for Chalmers' companies -- Bayoil...