Williamstown Theatre Festival has named Mandy Greenfield as its new Artistic Director, the Festival's Board Chair Matt Harris has announced.  Greenfield, who is currently Artistic Producer at Manhattan Theatre Club, succeeds Jenny Gersten beginning Sept 2014.  As previously announced, Gersten departs Williamstown Theatre Festival in Jan 2014 to become Executive Director of Friends of the Highline.  Gersten will program the upcoming 2014 season, and Williamstown Theatre Festival Producer Stephen Kaus will oversee the season. Greenfield's tenure as Artistic Director will begin immediately following the 2014 season, the Festival's 60th. Press contact: O&M Co (695-7400)...