Change the permission checks, provide distinct versions for Django 1.10+

private_storage/permissions.py

 """
 Possible functions for the ``PRIVATE_STORAGE_AUTH_FUNCTION`` setting.
 """
+import django
 
-
-def allow_authenticated(private_file):
-    try:
-        return private_file.request.user.is_authenticated()
-    except AttributeError:
-        # Using user.is_authenticated() and user.is_anonymous() as a method is deprecated since Django 2.0
+if django.VERSION >= (1, 10):
+    def allow_authenticated(private_file):
         return private_file.request.user.is_authenticated
-    
 
-def allow_staff(private_file):
-    request = private_file.request
-    try:
-        return request.user.is_authenticated() and request.user.is_staff
-    except AttributeError:
-        # Using user.is_authenticated() and user.is_anonymous() as a method is deprecated since Django 2.0
+    def allow_staff(private_file):
+        request = private_file.request
         return request.user.is_authenticated and request.user.is_staff
 
+    def allow_superuser(private_file):
+        request = private_file.request
+        return request.user.is_authenticated and request.user.is_superuser
+else:
+    def allow_authenticated(private_file):
+        return private_file.request.user.is_authenticated()
+
+    def allow_staff(private_file):
+        request = private_file.request
+        return request.user.is_authenticated() and request.user.is_staff
 
-def allow_superuser(private_file):
-    request = private_file.request
-    try:
+    def allow_superuser(private_file):
+        request = private_file.request
         return request.user.is_authenticated() and request.user.is_superuser
-    except AttributeError:
-        # Using user.is_authenticated() and user.is_anonymous() as a method is deprecated since Django 2.0
-        return request.user.is_authenticated and request.user.is_superuser