Capt. Stubing and his crew kick up their heels in a special two-hour musical extravaganza, ''The Love Boat Follies," a campy tribute to the "let's put on a show" movie musicals of yesteryear, with guest stars Cab Calloway, Carol Channing, Van Johnson, Ethel Merman, Ann Miller and Della Reese. These headliners - and all the series regulars.