Fix for DateTime superclass mismatch errors seen on some linux distributions. [Koz]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6121 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/lib/active_support/core_ext/date_time.rb

+require 'date'
 require "#{File.dirname(__FILE__)}/time/behavior"
 
-class DateTime
-  include ActiveSupport::CoreExtensions::Time::Behavior
-end
\ No newline at end of file
+DateTime.send(:include, ActiveSupport::CoreExtensions::Time::Behavior)