[Python-3000] Inclusion of the optimized C version of io.BytesIO into Py3K's trunk

[Alexandre Vassalotti]

Hello,

Since I am free today, I would like to merge my work on io.BytesIO
into Py3K's trunk. Antoine Pitrou reviewed my patch (see
http://bugs.python.org/issue1751) and concluded that the new module
looked fine. However, he couldn't say much about my changes to io.py
and _fileio.c (i.e., the semantic change of truncate to imply a seek).
So, I would appreciate it if someone would check io and _fileio fixes,
before I commit the patch.

Thank you,
-- Alexandre