clear warnings from MANIFEST.in

MANIFEST.in

@@ -2,7 +2,4 @@ include COPYING
 include NEWS
 include VERSION
 include tox.ini
-recursive-include tests *.py *.html
-recursive-include sample *.py *.html README *.py.example
-recursive-include src/django_gssapi/templates *.html
-recursive-include src/django_gssapi/static *.js
+recursive-include tests *.py

src/django_gssapi/backends.py

@@ -43,6 +43,7 @@ class GSSAPIBackend(object):
         else:
             if user.is_active:
                 return user
+        return None
 
 
 class KerberosPasswordBackend(object):
@@ -62,10 +63,10 @@ class KerberosPasswordBackend(object):
             user = User._default_manager.get_by_natural_key(username)
         except User.DoesNotExist:
             logger.debug('Kerberos: no user for username %s', username)
-            return
+            return None
         else:
             if not user.is_active:
-                return
+                return None
 
         principal = self.principal_from_user(user)
 
@@ -78,3 +79,4 @@ class KerberosPasswordBackend(object):
                 return user
         except gssapi.exceptions.GSSError as e:
             logger.debug('Kerberos: password check failed  for principal %s: %s', principal, e)
+        return None

tox.ini

@@ -34,9 +34,11 @@ commands =
     py.test {env:COVERAGE:} -o junit_suite_name={envname} --junit-xml=junit-{envname}.xml {posargs:tests}
 
 [testenv:pylint]
+basepython=python3
 deps =
-    pylint<1.8
-    pylint-django<0.8.1
+    pylint
+    pylint-django
+    django-rest-framework
 commands =
     pylint: ./pylint.sh src/django_gssapi/