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_xml_etree.py

@@ -39,14 +39,11 @@ def check_method(method):
     if not hasattr(method, '__call__'):
         print(method, "not callable")
 
-def serialize(ET, elem, encoding=None):
-    import StringIO
-    file = StringIO.StringIO()
+def serialize(ET, elem):
+    import io
     tree = ET.ElementTree(elem)
-    if encoding:
-        tree.write(file, encoding)
-    else:
-        tree.write(file)
+    file = io.StringIO()
+    tree.write(file)
     return file.getvalue()
 
 def summarize(elem):