Television is the most boundlessly nostalgic of mediums, perhaps because it has such a short memory. So when Andy Griffith brought back his old Mayberry sidekick, Don Knotts, to appear on his new show, Matlock, it set off this season’s avalanche of minireunions. Barbara (I Dream of Jeannie) Eden joined Larry Hagman on Dallas. Cagney and Lacey were together again when Tyne Daly showed up in a guest spot on Sharon Gless’s Trials of Rosie O’Neill. This week (March 18, 8:30 P.M. ET), Simon & Simon reincorporate when Jameson Parker turns up on Gerald McRaney’s solid CBS sitcom, Major Dad, as Polly’s old flame. If this trend continues, you can expect to see Tony Kubek elbowing aside Bryant Gumbel to join his old baseball-announcing partner, Joe Garagiola, on the Today show couch.