Fix SSL shutdown_transport function
Closes celery/#1414

In SSLTransport._read, errno.ENOENT must also be catched when reading
from the SSL socket. Moreover, it now uses an internal read buffer, as
in TCPTransport. This is done so that the both implementation are
coherent, but I don't really see the point as the OS already does
buffering!
Adds Adrien Guinet to AUTHORS