By Denny Dyroff, Entertainment Editor, The Times A great way to spend a warm summer evening is to sit in the audience at the Open Air Theater at Longwood Gardens (1001 Longwood Road, Kennett Square 610-388-1000, www.longwoodgardens.org) with a mild breeze blowing and the Kennett Symphony playing onstage, That scenario will exist on August 17.    Send article as PDF   ...