By Denny Dyroff, Entertainment Editor, The Times Jacqueline Kennedy Winterthur Museum, Garden & Library (Route 52, Wilmington, Delaware, 800-448-3883, www.winterthur.org) looks at American history with a new exhibit and Southern tradition with a special event tonight. On May 13, Winterthur will present a Kentucky influenced event called “Bourbon and Bluegrass.” Keeping the horse race vibe...