[1.6.x] Fixed a remote code execution vulnerabilty in URL reversing.

Thanks Benjamin Bach for the report and initial patch.

This is a security fix; disclosure to follow shortly.

Backport of 8b93b31487 from master

tests/urlpatterns_reverse/tests.py

@@ -1,8 +1,11 @@
+# -*- coding: utf-8 -*-
 """
 Unit tests for reverse URL lookups.
 """
 from __future__ import absolute_import, unicode_literals
 
+import sys
+
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
@@ -313,6 +316,25 @@ class ReverseShortcutTests(TestCase):
         self.assertEqual(res.url, '/foo/')
         res = redirect('http://example.com/')
         self.assertEqual(res.url, 'http://example.com/')
+        # Assert that we can redirect using UTF-8 strings
+        res = redirect('/æøå/abc/')
+        self.assertEqual(res.url, '/%C3%A6%C3%B8%C3%A5/abc/')
+        # Assert that no imports are attempted when dealing with a relative path
+        # (previously, the below would resolve in a UnicodeEncodeError from __import__ )
+        res = redirect('/æøå.abc/')
+        self.assertEqual(res.url, '/%C3%A6%C3%B8%C3%A5.abc/')
+        res = redirect('os.path')
+        self.assertEqual(res.url, 'os.path')
+
+    def test_no_illegal_imports(self):
+        # modules that are not listed in urlpatterns should not be importable
+        redirect("urlpatterns_reverse.nonimported_module.view")
+        self.assertNotIn("urlpatterns_reverse.nonimported_module", sys.modules)
+
+    def test_reverse_by_path_nested(self):
+        # Views that are added to urlpatterns using include() should be
+        # reversable by doted path.
+        self.assertEqual(reverse('urlpatterns_reverse.views.nested_view'), '/includes/nested_path/')
 
     def test_redirect_view_object(self):
         from .views import absolute_kwargs_view
@@ -641,4 +663,3 @@ class ViewLoadingTests(TestCase):
         # swallow it.
         self.assertRaises(AttributeError, get_callable,
             'urlpatterns_reverse.views_broken.i_am_broken')
-