Use the more appropriate columns_hash to get the session data column size limit.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2663 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

actionpack/lib/action_controller/session/active_record_store.rb

@@ -52,7 +52,7 @@ def reloadable? #:nodoc:
           end
           
           def data_column_size_limit
-            connection.columns(table_name).find {|column| column.name == 'data'}.limit
+            columns_hash['data'].limit
           end
 
           # Hook to set up sessid compatibility.