Revert "actually url helper are not used any way, so get rid of it..."

This reverts commit 5984438.

lib/big_sitemap.rb

@@ -324,10 +324,18 @@ def url_for_sitemap(path)
 
 class BigSitemapRails < BigSitemap
 
+  if defined?(Rails) && Rails.version < "3"
+    include ActionController::UrlWriter
+  end
+
   def initialize(options={})
     raise "No Rails Environment loaded" unless defined? Rails
     require 'action_controller'
 
+    if Rails.version >= "3"
+      self.class.send(:include, Rails.application.routes.url_helpers)
+    end
+
     DEFAULTS.merge!(:document_root => "#{Rails.root}/public", :url_options => default_url_options)
     super(options)
   end