Issue #13505: Make pickling of bytes object compatible with Python 2.

Initial patch by sbt.
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 49be720..cab0523 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -636,9 +636,15 @@
 
     def test_bytes(self):
         for proto in protocols:
-            for u in b'', b'xyz', b'xyz'*100:
-                p = self.dumps(u)
-                self.assertEqual(self.loads(p), u)
+            for s in b'', b'xyz', b'xyz'*100:
+                p = self.dumps(s)
+                self.assertEqual(self.loads(p), s)
+            for s in [bytes([i]) for i in range(256)]:
+                p = self.dumps(s)
+                self.assertEqual(self.loads(p), s)
+            for s in [bytes([i, i]) for i in range(256)]:
+                p = self.dumps(s)
+                self.assertEqual(self.loads(p), s)
 
     def test_ints(self):
         import sys