python - ex: Add Mapping class, and fix codes.

Log Message:
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Add Mapping class, and fix codes. Change the name of the PY code class to
PYTHON. It's not an acronym so there isnt much reason to keep it in short form.
Also, remove the PYTHON.CODE code. The Message class will no longer be doing
such extensive checks on the code that is given to __init__, so I don't think it
will be needed.
Give the Class type the ability to iterate over the registered states.
(Temporary breakage in prime.py)

Modified Files:
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    ex/src:
        code.py (r1.5 -> r1.6)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/ex/src/code.py.diff?r1=1.5&r2=1.6)