THE DOCUMENTARY "Nixon by Nixon: In His Own Words"; Monday night at 9 on HBO.WHAT IT'S ABOUT Peter Kunhardt's ("JFK: In His Own Words") documentary is based on 3,700 hours of secret recordings made by President Richard Nixon of phone conversations as well as those in the Oval Office, and other White House locations from 1971 to 1973. These recordings, known to only a few when they were made, have been studied by historians at the University of Virginia since 2000. Portions have been interwoven with archival footage and some of Nixon's post-White House inte...