Merged Rails 2.1 compatibility branch.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@1623 e93f8b46-1217-0410-a6f0-8f06a7374b81

vendor/plugins/acts_as_versioned/test/fixtures/widget.rb

@@ -1,6 +1,6 @@
 class Widget < ActiveRecord::Base
   acts_as_versioned :sequence_name => 'widgets_seq', :association_options => {
-    :dependent => nil, :order => 'version desc'
+    :dependent => :nullify, :order => 'version desc'
   }
   non_versioned_columns << 'foo'
 end