Plot: Gershwin's extrovert American in Paris is among the works that promise to make tonight's Promenade Concert one of the liveliest of the season. Also on the bill are Milhaud's exuberant Boeufsur le toit and the world premiere of Richard Rodney Bennett 's Concerto for Stan Getz , the composer's tribute to the late jazz saxophonist, featuring John Harle as soloist