Merge pull request #1380 from vijaydev/session_migration

Use 3.1 style migration for sessions table

activerecord/lib/rails/generators/active_record/session_migration/templates/migration.rb

 class <%= migration_class_name %> < ActiveRecord::Migration
-  def up
+  def change
     create_table :<%= session_table_name %> do |t|
       t.string :session_id, :null => false
       t.text :data
@@ -9,8 +9,4 @@ def up
     add_index :<%= session_table_name %>, :session_id
     add_index :<%= session_table_name %>, :updated_at
   end
-
-  def down
-    drop_table :<%= session_table_name %>
-  end
 end