Replaced many smart_bytes by force_bytes

In all those occurrences, we didn't care about preserving the
lazy status of the strings, but we really wanted to obtain a
real bytestring.

tests/regressiontests/admin_util/tests.py

@@ -171,7 +171,7 @@ class UtilTests(unittest.TestCase):
         )
         self.assertEqual(
             label_for_field("__str__", Article),
-            b"article"
+            str("article")
         )
 
         self.assertRaises(