Restores migration broken by r8182 and removes default scope on Role (#9800).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8213 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/020_add_role_position.rb

@@ -1,7 +1,7 @@
 class AddRolePosition < ActiveRecord::Migration
   def self.up
     add_column :roles, :position, :integer, :default => 1
-    Role.update_all("position = (SELECT COUNT(*) FROM #{Role.table_name} r WHERE r.id < id) + 1")
+    Role.all.each_with_index {|role, i| role.update_attribute(:position, i+1)}
   end
 
   def self.down