STINNER Victor (haypo)'s patch for bug 3988, Byte warning mode and b'' != ''

Also, his patch to runtests.sh to pass the -bb option (issue 4125).
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 81d2dad..c368143 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -9,6 +9,7 @@
 import re
 import sys
 import copy
+import operator
 import pickle
 import tempfile
 import unittest
@@ -863,6 +864,17 @@
         b = bytearray()
         self.failIf(b.replace(b'', b'') is b)
 
+    def test_compare(self):
+        if sys.flags.bytes_warning:
+            warnings.simplefilter('error', BytesWarning)
+            self.assertRaises(BytesWarning, operator.eq, b'', '')
+            self.assertRaises(BytesWarning, operator.ne, b'', '')
+            self.assertRaises(BytesWarning, operator.eq, bytearray(b''), '')
+            self.assertRaises(BytesWarning, operator.ne, bytearray(b''), '')
+        else:
+            # raise test.support.TestSkipped("BytesWarning is needed for this test: use -bb option")
+            pass
+
     # Optimizations:
     # __iter__? (optimization)
     # __reversed__? (optimization)