NotFound.rest_of_name always just contains 1 component. It should instead
contain *all* components that were not resolved.

Also, when 'why' is 'not_context', rest_of_name contains
the item that is not a context. Why is that? That component has
already been resolved. rest_of_name should only contain
components that have not been resolved. It would be very useful
for to be able to depend upon the fact that rest_of_name consistently contains
the portion of the name not found, rather than forcing the caller
to check 'why'.

Also, it would also be very useful if NotFound has a 'resolved object' field.
In throwing the exception, the server must have already have this information.