Refactor code just a little bit

lib/paperclip.rb

@@ -179,10 +179,8 @@ module Paperclip
   module Glue
     def self.included base #:nodoc:
       base.extend ClassMethods
-      if base.respond_to?("class_attribute")
-        base.class_attribute :attachment_definitions
-      end
-      if base.respond_to?("set_callback")
+      base.class_attribute :attachment_definitions if base.respond_to?(:class_attribute)
+      if base.respond_to?(:set_callback)
         base.send :include, Paperclip::CallbackCompatability::Rails3
       else
         base.send :include, Paperclip::CallbackCompatability::Rails21