os.py: do not import gevent.socket

since gevent.os is imported in __init__.py this makes gevent.socket imported in __init__.py which was never the intention.

gevent/os.py

@@ -9,9 +9,10 @@ from __future__ import absolute_import
 import os
 import sys
 from gevent.hub import get_hub, reinit
-from gevent.socket import EAGAIN
 import errno
 
+EAGAIN = getattr(errno, 'EAGAIN', 11)
+
 try:
     import fcntl
 except ImportError: