version 3.3.4, more specifically identify nonblocking read errors

versions 3.3.1, 3.3.2 and 3.3.3 could potentially hide ConnectionErrors
on Python 2.7. This change accurately identifies errors by both
exception class and errno to determine whether a nonblocking socket can
be read

Author: andymccurdy

redis/connection.py

@@ -2,6 +2,7 @@
 from distutils.version import StrictVersion
 from itertools import chain
 from time import time
+import errno
 import io
 import os
 import socket
@@ -35,7 +36,7 @@
     ssl_available = False
 
 NONBLOCKING_EXCEPTION_ERROR_NUMBERS = {
-    BlockingIOError: 35,
+    BlockingIOError: errno.EWOULDBLOCK,
 }
 
 if ssl_available: