python 3, subclassing TextIOWrapper.

[lambertdw at corning.com]

For D. Murray's suggestion---I think that we programmers have to learn
the idiom.  We don't always control open, such as subprocess.Popen().

Thank you.  I hope these thoughts help with issue 5513 and the related
questions to follow about complete removal of file in python3.
Opening the file in binary mode for text behavior was not obvious to
me, but makes good sense now that you've explained the further
nesting.