Make Rake::DSL methods available within Railtie rake_tasks block

Fixes incompatibility introduced by Rake 0.9.0

railties/lib/rails/application.rb

@@ -185,10 +185,12 @@ module Rails
     end
 
     def initialize_tasks
-      require "rails/tasks"
-      task :environment do
-        $rails_rake_task = true
-        require_environment!
+      self.class.rake_tasks do
+        require "rails/tasks"
+        task :environment do
+          $rails_rake_task = true
+          require_environment!
+        end
       end
     end
 

railties/lib/rails/railtie.rb

@@ -178,6 +178,7 @@ module Rails
     end
 
     def load_tasks
+      extend Rake::DSL if defined? Rake::DSL
       self.class.rake_tasks.each(&:call)
 
       # load also tasks from all superclasses