Four days before the May 27 airing of “Innocence Lost: The Plea,” Frontline’s third documentary on the Little Rascals child-abuse case in Edenton, N.C., the prosecutor announced she was dropping all remaining charges in the long and troubling legal action. For producer-director Ofra Bikel and her colleagues at Frontline, the decision brought a rare sense of gratification. Over the past seven years, Bikel’s persistent scrutiny of a prosecution she had come to believe was unjust has made a big difference in many people’s lives. Whether the effect has been for the better or the worse depends on how close you live to Edenton, and which side of the Little Rascals case you want to believe. “It’s not very often that a television program can set people free,” commented David Fanning, Frontline’s senior executive producer.