Correct docs for ABCs (MutableSequence was missing __setiem).  Simplify the table by taking out inherited requirements for abstract methods.

been done purely to help transitions from 2.7 to 3.1.

Properly document multiprocessing's logging support, resolve outstanding issues with the custom levels

with manually specified, conflicting names.

Before:
    http://docs.python.org/dev/library/collections.html#id1

After:
    http://docs.python.org/dev/library/collections.html#counter-objects

* Constructor and update() support keyword args (like their dict counterparts).
* The 'del' statement no longer raises KeyError for missing values.
* Add multiset operations:  __add__, __sub__, __and__, __or__.

pasted and changed afterwards.