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_threadedtempfile.py

@@ -22,7 +22,7 @@ import tempfile
 
 from test.test_support import threading_setup, threading_cleanup, run_unittest
 import unittest
-import StringIO
+import io
 from traceback import print_exc
 
 startEvent = threading.Event()
@@ -32,7 +32,7 @@ class TempFileGreedy(threading.Thread):
     ok_count = 0
 
     def run(self):
-        self.errors = StringIO.StringIO()
+        self.errors = io.StringIO()
         startEvent.wait()
         for i in range(FILES_PER_THREAD):
             try: