use class_attribute instead of class_inheritable_attribute

lib/paperclip.rb

@@ -160,6 +160,8 @@ class InfiniteInterpolationError < PaperclipError #:nodoc:
   module Glue
     def self.included base #:nodoc:
       base.extend ClassMethods
+      base.class_attribute :attachment_definitions
+
       if base.respond_to?("set_callback")
         base.send :include, Paperclip::CallbackCompatability::Rails3
       else
@@ -235,7 +237,7 @@ module ClassMethods
     def has_attached_file name, options = {}
       include InstanceMethods
 
-      write_inheritable_attribute(:attachment_definitions, {}) if attachment_definitions.nil?
+      self.attachment_definitions = {} if attachment_definitions.nil?
       attachment_definitions[name] = {:validations => []}.merge(options)
 
       after_save :save_attached_files
@@ -339,12 +341,6 @@ def validates_attachment_content_type name, options = {}
         end
       end
     end
-
-    # Returns the attachment definitions defined by each call to
-    # has_attached_file.
-    def attachment_definitions
-      read_inheritable_attribute(:attachment_definitions)
-    end
   end
 
   module InstanceMethods #:nodoc: