When you first heard it, you couldn't believe it: Jerry Mathers, from TV's "Leave It To Beaver," had been killed in Vietnam. Then word came that Abe Vigoda, the actor who played the curmudgeonly cop Fish on "Barney Miller," was dead; and that Mikey, who would eat anything as the Life Cereal tyke, had eaten too many Pop Rocks and exploded. Besides exposing us to things we couldn't otherwise believe, television can convince us of things that never actually happened. But how did these outrageous TV legends get started? How did they spread from classrooms to boardrooms across North America and...