------------------
- Fix a bug in the default ordering that would cause the ``pos`` dict to get
out of sync when an item is deleted.
[optilude]
- Declare ``IContainer`` support.
[optilude]
- Properly set ``__parent__`` and ``__name__`` for ``IContained`` in
``_setOb()``.
[optilude]
- Add ``__getitem__``, needed when not using the CMF mix-in.
[optilude]
- Added ``__setitem__``, ``__contains__`` and ``__delitem__`` to support a
dict-like API.
[optilude]
- Fix issue with removing non-orderable content for partial ordering suppport.
[witsch]
- Fix ``getObjectPosition`` to return a value representing "no position" for
non-orderable content instead of raising an error.
[witsch]
- Fix boolean value of the btree-based folder base class.
[witsch]
- Factor CMF out of the base classes for the new btree-based folder class
and simplify things a bit afterwards.
[witsch]
- Add adapter providing explicit ordering only for "orderable" content.
[witsch]
- Clean up tests and their setup.
[witsch]