pass new config options to chunky_png canvas on image save

lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb

@@ -33,7 +33,8 @@ module Compass
           if canvas.nil?
             construct_sprite
           end
-          canvas.save(filename, :best_compression)
+          
+          canvas.save(filename,  Compass.configuration.chunky_png_options)
         end
         
       end