Merge remote-tracking branch 'core/master' into schema-alteration

Conflicts:
	django/db/backends/__init__.py
	django/db/models/fields/related.py
	tests/field_deconstruction/tests.py

django/test/utils.py

@@ -10,6 +10,7 @@ from django.conf import settings, UserSettingsHolder
 from django.core import mail
 from django.core.signals import request_started
 from django.db import reset_queries
+from django.http import request
 from django.template import Template, loader, TemplateDoesNotExist
 from django.template.loaders import cached
 from django.test.signals import template_rendered, setting_changed
@@ -87,13 +88,16 @@ def setup_test_environment():
         - Set the email backend to the locmem email backend.
         - Setting the active locale to match the LANGUAGE_CODE setting.
     """
-    Template.original_render = Template._render
+    Template._original_render = Template._render
     Template._render = instrumented_test_render
 
-    mail.original_email_backend = settings.EMAIL_BACKEND
+    # Storing previous values in the settings module itself is problematic.
+    # Store them in arbitrary (but related) modules instead. See #20636.
+
+    mail._original_email_backend = settings.EMAIL_BACKEND
     settings.EMAIL_BACKEND = 'django.core.mail.backends.locmem.EmailBackend'
 
-    settings._original_allowed_hosts = settings.ALLOWED_HOSTS
+    request._original_allowed_hosts = settings.ALLOWED_HOSTS
     settings.ALLOWED_HOSTS = ['*']
 
     mail.outbox = []
@@ -108,14 +112,14 @@ def teardown_test_environment():
         - Restoring the email sending functions
 
     """
-    Template._render = Template.original_render
-    del Template.original_render
+    Template._render = Template._original_render
+    del Template._original_render
 
-    settings.EMAIL_BACKEND = mail.original_email_backend
-    del mail.original_email_backend
+    settings.EMAIL_BACKEND = mail._original_email_backend
+    del mail._original_email_backend
 
-    settings.ALLOWED_HOSTS = settings._original_allowed_hosts
-    del settings._original_allowed_hosts
+    settings.ALLOWED_HOSTS = request._original_allowed_hosts
+    del request._original_allowed_hosts
 
     del mail.outbox
 
@@ -207,7 +211,6 @@ class override_settings(object):
     """
     def __init__(self, **kwargs):
         self.options = kwargs
-        self.wrapped = settings._wrapped
 
     def __enter__(self):
         self.enable()
@@ -246,6 +249,7 @@ class override_settings(object):
         override = UserSettingsHolder(settings._wrapped)
         for key, new_value in self.options.items():
             setattr(override, key, new_value)
+        self.wrapped = settings._wrapped
         settings._wrapped = override
         for key, new_value in self.options.items():
             setting_changed.send(sender=settings._wrapped.__class__,
@@ -253,6 +257,7 @@ class override_settings(object):
 
     def disable(self):
         settings._wrapped = self.wrapped
+        del self.wrapped
         for key in self.options:
             new_value = getattr(settings, key, None)
             setting_changed.send(sender=settings._wrapped.__class__,