use plain Ruby memoization to fix deprecation (closes #121)

app/models/article.rb

@@ -1,6 +1,5 @@
 # encoding: utf-8
 class Article < ActiveRecord::Base
-  extend ActiveSupport::Memoizable    # Ability to cache method results. Use memoize :expensive_method
 
   # Replace numeric seperator with database format
   localize_input_of :price, :tax, :deposit
@@ -44,11 +43,12 @@ class Article < ActiveRecord::Base
   
   # If the article is used in an open Order, the Order will be returned.
   def in_open_order
+    @in_open_order ||= begin
       order_articles = OrderArticle.all(:conditions => ['order_id IN (?)', Order.open.collect(&:id)])
       order_article = order_articles.detect {|oa| oa.article_id == id }
       order_article ? order_article.order : nil
     end
-  memoize :in_open_order
+  end
   
   # Returns true if the article has been ordered in the given order at least once
   def ordered_in_order?(order)

app/models/group_order_article.rb

@@ -2,7 +2,6 @@
 # The chronologically order of the Ordergroup - activity are stored in GroupOrderArticleQuantity
 #
 class GroupOrderArticle < ActiveRecord::Base
-  extend ActiveSupport::Memoizable    # Ability to cache method results. Use memoize :expensive_method
 
   belongs_to :group_order
   belongs_to :order_article
@@ -101,6 +100,7 @@ class GroupOrderArticle < ActiveRecord::Base
   # 
   # See description of the ordering algorithm in the general application documentation for details.
   def calculate_result
+    @calculate_result ||= begin
       quantity = tolerance = 0
       stockit = order_article.article.is_a?(StockArticle)
 
@@ -148,7 +148,7 @@ class GroupOrderArticle < ActiveRecord::Base
 
       {:quantity => quantity, :tolerance => tolerance, :total => quantity + tolerance}
     end
-  memoize :calculate_result
+  end
 
   # Returns order result,
   # either calcualted on the fly or fetched from result attribute