[issue19697] Document the possible values for __main__.__spec__

[Roundup Robot]

Roundup Robot added the comment:

New changeset 4972475ae2e7 by Eric Snow in branch '3.4':
Issue #19697: Document cases where __main__.__spec__ is None.
http://hg.python.org/cpython/rev/4972475ae2e7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue19697>
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