Restore SSL_shutdown() two step sequence.

Restore SSL_shutdown() two step sequence.

Change SSL_shutdown() such that it will return 0 after sending a
close-notify, before potentially returning 1 (indicating that a
close-notify has been sent and received) on a subsequent call. Some
software depends on this behaviour, even though there are cases where
the first call could immediately return 1 (for example, when the peer
has already sent a close-notify prior to SSL_shutdown() being called).

ok tb@