* Access rights are checked before the storage is locked and
collections are loaded.
* DELETE sends 410 instead of doing nothing or crashing if the target
doesn't exist.
* GET always returns 404 if the target doesn't exist.
* GET doesn't crash if a collection without tag property is requested.
* MKCOL and MKCALENDAR send 409 if the target already exists.
* MOVE checks if the target collection of an item actually exists and
sends 409 otherwise.
* PUT doesn't crash if a whole collection that doesn't exist yet is
uploaded and ``content-type`` is ``text/vcard`` or
``text/calendar``.
* PUT distinguishes between simple items and whole collections by the
following criteria: Target is a collection; Parent exists; Parent
has the tag property set; Parent contains other items. Before only
the first two criteria where used, which was very unrelieable. #384
* PROPPATCH is only allowed on collections and 409 is send otherwise.
* ``Rights.authorized`` takes a path instead of a collection.
* ``Collection.discover`` only returns items in ``path``, that
actually exist. #442
