Convert the socket module to insist on bytes for input, and to return bytes
(not bytearray) on output.  Discovered a bunch of places that were still
depending on it accepting text strings.
diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py
index ef8565c..983cf21 100644
--- a/Lib/test/test_poplib.py
+++ b/Lib/test/test_poplib.py
@@ -19,7 +19,7 @@
     except socket.timeout:
         pass
     else:
-        conn.send("+ Hola mundo\n")
+        conn.send(b"+ Hola mundo\n")
         conn.close()
     finally:
         serv.close()