Fixed crash comparing CheckMessage objects to non-CheckMessage objects.

django/core/checks/messages.py

@@ -23,8 +23,11 @@ class CheckMessage(object):
         self.id = id
 
     def __eq__(self, other):
-        return all(getattr(self, attr) == getattr(other, attr)
-                   for attr in ['level', 'msg', 'hint', 'obj', 'id'])
+        return (
+            isinstance(other, self.__class__) and
+            all(getattr(self, attr) == getattr(other, attr)
+                for attr in ['level', 'msg', 'hint', 'obj', 'id'])
+        )
 
     def __ne__(self, other):
         return not (self == other)

tests/check_framework/tests.py

@@ -124,6 +124,10 @@ class MessageTests(SimpleTestCase):
         e2 = Error("Error2", obj=SimpleModel)
         self.assertNotEqual(e1, e2)
 
+    def test_not_equal_to_non_check(self):
+        e = Error("Error", obj=DummyObj())
+        self.assertNotEqual(e, 'a string')
+
 
 def simple_system_check(**kwargs):
     simple_system_check.kwargs = kwargs