Fixing issue #534 (now it works on Rails 2.3.8)

Closes #534, closes #538

lib/paperclip.rb

@@ -179,7 +179,9 @@ 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.send :include, Paperclip::CallbackCompatability::Rails3
       else