Consistent hashing of the Sprite importer object

lib/compass/sass_extensions/sprites/sprites.rb

@@ -49,5 +49,14 @@ module Compass
     def to_s
       ""
     end
+
+    def hash
+      self.class.name.hash
+    end
+
+    def eql?(other)
+      other.class == self.class
+    end
+
   end
 end