dbm.gnu and dbm.ndbm accept both strings and bytes as keys and values. For the
former they are converted to bytes before being written to the DB.

Closes issue 3799. Reviewed by Skip Montanaro.
diff --git a/Lib/test/test_dbm_dumb.py b/Lib/test/test_dbm_dumb.py
index 940991d..e2964aa 100644
--- a/Lib/test/test_dbm_dumb.py
+++ b/Lib/test/test_dbm_dumb.py
@@ -115,11 +115,13 @@
         self.init_db()
         f = dumbdbm.open(_fname)
         f['\u00fc'] = b'!'
+        f['1'] = 'a'
         f.close()
         f = dumbdbm.open(_fname, 'r')
         self.assert_('\u00fc' in f)
         self.assertEqual(f['\u00fc'.encode('utf-8')],
                          self._dict['\u00fc'.encode('utf-8')])
+        self.assertEqual(f[b'1'], b'a')
 
     def test_line_endings(self):
         # test for bug #1172763: dumbdbm would die if the line endings