uninitialized constant ActionController::Dispatcher (NameError) with Rails 1.2.3, 1.2.6

Whilst migrating an old application for a client then I stumbled across a problem getting it to work with Thin - the application is still running Rails 1.2.6 and when combined with Thin it was not starting, giving:

/var/rails/older/vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:266:in load_missing_constant': uninitialized constant ActionController::Dispatcher (NameError)

I seem to remember Dispatcher (in 1.2.x days) was moved to ActionController::Dispatcher, so it fails to start as it can't perform the check on ActionController::Dispatcher in Rails 1.2.x applications. I've modified the rails rack adapter to check if ActionController::Dispatcher is defined and this does the trick and allows Thin to load the application -

http://gist.github.com/145594