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_codeop.py

@@ -6,10 +6,10 @@ import unittest
 from test.test_support import run_unittest, is_jython
 
 from codeop import compile_command, PyCF_DONT_IMPLY_DEDENT
+import io
 
 if is_jython:
     import sys
-    import cStringIO
 
     def unify_callables(d):
         for n,v in d.items():
@@ -27,7 +27,7 @@ class CodeopTests(unittest.TestCase):
             if symbol == "single":
                 d,r = {},{}
                 saved_stdout = sys.stdout
-                sys.stdout = cStringIO.StringIO()
+                sys.stdout = io.StringIO()
                 try:
                     exec(code, d)
                     exec(compile(str,"<input>","single"), r)