diff --git a/django/core/management/base.py b/django/core/management/base.py
index a204f6f0bcb..5e630d52070 100644
--- a/django/core/management/base.py
+++ b/django/core/management/base.py
@@ -6,7 +6,6 @@ be executed through ``django-admin.py`` or ``manage.py``).
 import os
 import sys
 
-from io import BytesIO
 from optparse import make_option, OptionParser
 import traceback
 
@@ -14,6 +13,7 @@ import django
 from django.core.exceptions import ImproperlyConfigured
 from django.core.management.color import color_style
 from django.utils.encoding import smart_str
+from django.utils.six import StringIO
 
 
 class CommandError(Exception):
@@ -273,7 +273,7 @@ class BaseCommand(object):
 
         """
         from django.core.management.validation import get_validation_errors
-        s = BytesIO()
+        s = StringIO()
         num_errors = get_validation_errors(s, app)
         if num_errors:
             s.seek(0)
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 4568430bfaf..35ae2231d66 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -28,6 +28,30 @@ from django.utils import six
 from django.utils.text import get_text_list, capfirst
 
 
+def subclass_exception(name, parents, module, attached_to=None):
+    """
+    Create exception subclass. Used by ModelBase below.
+
+    If 'attached_to' is supplied, the exception will be created in a way that
+    allows it to be pickled, assuming the returned exception class will be added
+    as an attribute to the 'attached_to' class.
+    """
+    class_dict = {'__module__': module}
+    if attached_to is not None:
+        def __reduce__(self):
+            # Exceptions are special - they've got state that isn't
+            # in self.__dict__. We assume it is all in self.args.
+            return (unpickle_inner_exception, (attached_to, name), self.args)
+
+        def __setstate__(self, args):
+            self.args = args
+
+        class_dict['__reduce__'] = __reduce__
+        class_dict['__setstate__'] = __setstate__
+
+    return type(name, parents, class_dict)
+
+
 class ModelBase(type):
     """
     Metaclass for all models.
@@ -929,29 +953,6 @@ def model_unpickle(model, attrs):
     return cls.__new__(cls)
 model_unpickle.__safe_for_unpickle__ = True
 
-def subclass_exception(name, parents, module, attached_to=None):
-    """
-    Create exception subclass.
-
-    If 'attached_to' is supplied, the exception will be created in a way that
-    allows it to be pickled, assuming the returned exception class will be added
-    as an attribute to the 'attached_to' class.
-    """
-    class_dict = {'__module__': module}
-    if attached_to is not None:
-        def __reduce__(self):
-            # Exceptions are special - they've got state that isn't
-            # in self.__dict__. We assume it is all in self.args.
-            return (unpickle_inner_exception, (attached_to, name), self.args)
-
-        def __setstate__(self, args):
-            self.args = args
-
-        class_dict['__reduce__'] = __reduce__
-        class_dict['__setstate__'] = __setstate__
-
-    return type(name, parents, class_dict)
-
 def unpickle_inner_exception(klass, exception_name):
     # Get the exception class from the class it is attached to:
     exception = getattr(klass, exception_name)
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 2c738d6a20f..2c38e8d72e0 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -135,6 +135,8 @@ class Field(object):
             return self.creation_counter < other.creation_counter
         return NotImplemented
 
+    __hash__ = object.__hash__
+
     def __deepcopy__(self, memodict):
         # We don't have to deepcopy very much here, since most things are not
         # intended to be altered after initial creation.
diff --git a/django/test/client.py b/django/test/client.py
index ef80a7129a3..a9ae7f5db10 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -194,9 +194,9 @@ class RequestFactory(object):
             'SERVER_NAME':       'testserver',
             'SERVER_PORT':       '80',
             'SERVER_PROTOCOL':   'HTTP/1.1',
-            'wsgi.version':      (1,0),
+            'wsgi.version':      (1, 0),
             'wsgi.url_scheme':   'http',
-            'wsgi.input':        FakePayload(''),
+            'wsgi.input':        FakePayload(b''),
             'wsgi.errors':       self.errors,
             'wsgi.multiprocess': True,
             'wsgi.multithread':  False,