introduce the six module and reduce sphinx.util.pycompat implementation. refs #1350.

tests/util.py

@@ -8,12 +8,13 @@
 """
 
 import sys
-import StringIO
 import tempfile
 import shutil
 import re
 from functools import wraps
 
+import six
+
 from sphinx import application
 from sphinx.theming import Theme
 from sphinx.ext.autodoc import AutoDirective
@@ -162,7 +163,7 @@ class TestApp(application.Sphinx):
         if confoverrides is None:
             confoverrides = {}
         if status is None:
-            status = StringIO.StringIO()
+            status = six.StringIO()
         if warning is None:
             warning = ListOutput('stderr')
         if freshenv is None: