failing tests for containsNode; refactor tests

reduntant test for unique ids was removed.

tree.containsNode does not throw errors as it should on
non-nodes. This will be fixed next.
fix containsNode throws; bump verstion to v0.2.2

backwards-compatible bug fix, thus the patch version bump.

I'd like to do without explicit throws, but stuff like `(0).__tree`
doesn't throw on its own, while `(null).__tree` does.

A test for tree.walk was setup wrong, so that is fixed as well.