controller_relative_to

# File actionpack/lib/action_controller/routing.rb, line 310
      def controller_relative_to(controller, previous)
        if controller.nil?           then previous
        elsif controller[0] == ?/    then controller[1..-1]
        elsif %r{^(.*)/} =~ previous then "#{$1}/#{controller}"
        else controller
        end     
      end