Say it isn't so! Since 1966 Charlie Brown's "The Great Pumpkin" has aired annually entertaining children and parents. But in this week's airing it was thumped by a Two-hour episodes of NBC's weight-loss reality show "The Biggest Loser" (3.7/10) and Fox's "So You Think You Can Dance" (2.5/6). (CBS and the CW ran reruns of "NCIS," 3.3/9 and "90210," .6/2.) The times they are a changing.