[docs] [issue12148] Clarify "or-ing together" doctest option flags

[Terry J. Reedy]

Changes by Terry J. Reedy <tjreedy at udel.edu>:


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versions: +Python 3.4, Python 3.5 -Python 3.1, Python 3.2, Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12148>
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