bad redirect for applications deployed to sub-uri

This is a minute problem but if you have an application deployed to a sub-uri say

config.action_controller.relative_url_root = "/example"

restful_authentication will by default redirect to the root of the server instead of the root of the application:

def destroy
  logout_killing_session!
  flash[:notice] = "You have been logged out."
  redirect_back_or_default('/')
end

this same behaviour occurs in several places

I could not find how to specifically specify the root url of the application, I used root_url, which requires the map.root route to be set.