SF patch# 1770008 by Christian Heimes (plus some extras).

Completely get rid of StringIO.py and cStringIO.c.

I had to fix a few tests and modules beyond what Christian did, and
invent a few conventions.  E.g. in elementtree, I chose to
write/return Unicode strings whe no encoding is given, but bytes when
an explicit encoding is given.  Also mimetools was made to always
assume binary files.

Lib/test/test_optparse.py

@@ -14,7 +14,7 @@ import re
 import copy
 import unittest
 
-from StringIO import StringIO
+from io import StringIO
 from pprint import pprint
 from test import test_support
 
@@ -157,12 +157,9 @@ and kwargs %(kwargs)r
                      expected_error=None):
         """Assert the parser prints the expected output on stdout."""
         save_stdout = sys.stdout
-        encoding = getattr(save_stdout, 'encoding', None)
         try:
             try:
                 sys.stdout = StringIO()
-                if encoding:
-                    sys.stdout.encoding = encoding
                 self.parser.parse_args(cmdline_args)
             finally:
                 output = sys.stdout.getvalue()