default namespace devise problem

I have a Problem with the `default_namespace` config option.

Without any config change, the routes are:
```
new_user_session_path	 	GET		/admin/login(.:format)
new_admin_customer_path	GET		/admin/customers/new(.:format)
```

With `config.default_namespace = false` the routes are:
```
new_user_session_path		GET		/users/login(.:format)
customers_path	 		GET		/customers(.:format)
```

But I think the routes should be:
```
new_user_session_path		GET		/login(.:format)
customers_path	 		GET		/customers(.:format)
```