[py3] Switched to Python 3-compatible imports.

xrange/range will be dealt with in a separate commit due to the huge
number of changes.

django/test/_doctest.py

@@ -103,9 +103,9 @@ import __future__
 import sys, traceback, inspect, linecache, os, re
 import unittest, difflib, pdb, tempfile
 import warnings
-from StringIO import StringIO
 
 from django.utils import six
+from django.utils.six import StringIO
 
 if sys.platform.startswith('java'):
     # On Jython, isclass() reports some modules as classes. Patch it.

django/test/html.py

@@ -5,9 +5,8 @@ Comparing two html documents.
 from __future__ import unicode_literals
 
 import re
-from HTMLParser import HTMLParseError
 from django.utils.encoding import force_unicode
-from django.utils.html_parser import HTMLParser
+from django.utils.html_parser import HTMLParser, HTMLParseError
 from django.utils import six