Festival setThe annual Mississippi River Festival held at the Ed-wardsville campus of Southern Illinois University has just released its roster of signed talent slated to perform June 13| through August 25. Onstage for the com posit music bash are: Andy Gibb, America, Dolly Par-ton, Chuck Mangione, Leo Sayer, the Doobie Brothers, Kenny Loggins, Phoebe Snow, Harry Chapin, Peter. Paul and Mary, Sha Na Na. Mac Davis, and dozens of other recording artists and groups. Tickets for concerts range from $5 to $7.50.