Change ssl to return a socket.timeout exception on timeout instead of…

… an SSLError

Back in Python 3.2, ssl.SSLError used to be a subclass of socket.error (see
https://docs.python.org/3/library/ssl.html#exceptions), so timeouts on
monkeypatched ssl sockets would be properly caught by socket.timeout
excpetion handlers in applications.  However, since Python 3.3 ssl.SSLerror
is a subclass of OSError, which signifies a different (typically fatal)
type of error that is usually not handled gracefully by applications.

By changing the timeout excpetion back to socket.timeout, libraries such
as pymysql and redis will again properly support TLS-connections in
monkeypatched apoplications.

eventlet/green/ssl.py

@@ -15,7 +15,7 @@
 
 orig_socket = __import__('socket')
 socket = orig_socket.socket
-timeout_exc = SSLError
+timeout_exc = orig_socket.timeout
 
 __patched__ = [
     'SSLSocket', 'SSLContext', 'wrap_socket', 'sslwrap_simple',