Fix NotImplemented into NotImplementedError

(transplanted from a1bd31febf2954da49303b3e1e490a714a98ebb4)

proteus/config.py

@@ -51,7 +51,7 @@ class Config(object):
     def __eq__(self, other):
         if isinstance(other, Config):
             return repr(self) == repr(other)
-        return NotImplemented
+        return NotImplementedError
 
 
 class _TrytondMethod(object):

proteus/tests/test_config.py

@@ -26,4 +26,4 @@ class TestConfig(TestCase):
         config2 = proteus.config.get_config()
         self.assertEqual(config1, config2)
 
-        self.assertEqual(config1.__eq__(None), NotImplemented)
+        self.assertRaises(NotImplementedError, config1.__eq__, None)