[issue25315] Make it clear in the OrderedDict source that it may be overridden

[R. David Murray]

Changes by R. David Murray <rdmurray at bitdance.com>:


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title: OrderedDict mangled private attribute is inaccessible -> Make it clear in the OrderedDict source that it may be overridden

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25315>
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