Introduced AclWrappedNewRevision in order to detect changes on an items ACL metadata value. We shouldn't need to wrap around StoredRevision as well since objects thereof are already immutable.
NB: Item and Revision both inherit from DictMixin which provides further methods. Afaict, these are all based on getitem, setitem and delitem. Hence it should be sufficient to implement those on the AMW level and just make the proxies inherit from DictMixin as well.
- Provided default message string 'Permission denied!' for ADError
- For has_item we now just pass through to the real backend, hence not hiding the sheer existance of any item.
See: