Treat ssl.SSL_ERROR_WANT_WRITE and ssl.SSL_ERROR_WANT_READ like EAGAIN

According to [here](http://stackoverflow.com/questions/3952104/how-to-handle-openssl-ssl-error-want-read-want-write-on-non-blocking-sockets), you can get `SSL_WANT_READ` or `SSL_WANT_WRITE` from either read or write calls, so you may want to catch all 3 here.