At some point in their military career, U.S. troops will likely hear the rumor that television's Mr. Rogers, host of "Mister Rogers' Neighborhood," was a death-dealing, hardcore Vietnam-era sniper in either the Army Special Forces, Navy SEALs, or the Marine Corps.  Fred Rogers and his past are just one more file to add to the mounting list of military myths and urban legends. It might be fun to think of a man as smart and wholesome as Fred Rogers picking off a North Vietnamese general or...