[issue15381] Optimize BytesIO to do less reallocations when written, similarly to StringIO

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Synchronized with tip. Unfortunately there are no common points with recent issue22003 changes so they should be reverted (except tests).

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versions: +Python 3.5 -Python 3.4
Added file: http://bugs.python.org/file36180/bytesio_resized_bytes-4.patch

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<http://bugs.python.org/issue15381>
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