[docs] [issue24800] exec docs should note that the no argument form in a local scope is really the two argument form

[R. David Murray]

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


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versions: +Python 3.5, Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24800>
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