HUNTSVILLE, Texas — A man who experts for both prosecutors and defense attorneys had said was intellectually disabled became the 600th person executed in Texas since 1982, put to death Thursday evening for the killing of a 77-year-old retired college professor. Edward Busby Jr. was pronounced dead at 8:11 p.m. following a lethal injection at the state penitentiary in Huntsville, hours after the U.S. Supreme Court lifted a stay over his disabilities claims. The execution capped a series of last-