Test that unknown root files return 404
Don't attempt to get es doc in the Root controller

The parent class has a default action but dies because the Root controller
has no 'type', so just skip the logic and go straight to 404.

This fixes the previously added test.
Explicitly test 404 on a non-root (non-existent) url
Make the default message "Not found" instead of the path

Getting a message of just "path/part" is confusing and unhelpful.
This is now consistent with when the type is correct but a doc isn't found.
Remove unused message argument from not_found tests

It hasn't been used in a long time
and now we can expect the same message from everywhere.
Comment on why test suite says "mapping" for all scripts