Breaking changes, sorry. Also remade the SceneTools hierarchy test to
not be that much redundant -- the name- and ID-based overloads can be
tested together.
These don't copy the data but rather reference the original with
different metadata. That caused use-after-free originally (if the input
variable got deleted or overwritten), the previous commit made it
assert (which was the intention there). Now it works properly.
Vladimír Vondruš