No joking, just yodeling. Well, actually, there’ll probably be both when Wylie Gustafson, the YODELING COWBOY who made famous his catchy and drawn-out signature “Ya-Hoo-Ooo,” appears on late-night TV tomorrow (April 1). Everyone’s favorite singer, songwriter, horseman and original Yahoo yodeler is scheduled to appear on “LATE NIGHT WITH CONAN O’BRIEN” on April Fool’s Day. [...]