Merged revisions 76805 via svnmerge from

Merged revisions 76805 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

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  r76805 | benjamin.peterson | 2009-12-13 13:19:07 -0600 (Sun, 13 Dec 2009) | 7 lines

  accept None as the same as having passed no argument in file types #7349

  This is for consistency with imitation file objects like StringIO and BytesIO.

  This commit also adds a few tests, where they were lacking for concerned
  methods.
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