[Python-Dev] ABC issues

[Georg Brandl]

Some ABC issues:

* The 2.6-backported Mapping ABC has the 3.0 dict API,
   that is, it uses keys() that returns a view etc.

* The 2.6 UserDict is not registered as a mapping.

* collections.deque isn't registered as a MutableSequence.

If there are no objections, I will correct these issues
in the 2.6 and 3.0 branches.

Georg