The existing --ftp-ssl option will revert to a non-SSL transfer if the
Server doesn't support SSL/TLS.

I'm proposing a new --ftp-ssl-reqd option that will perform the transfer
only if the AUTH SSL/TLS succeeds on both the control and data connections.
(It sets CURLFTPSSL_ALL instead of CURLFTPSSL_TRY.)

The patch is attached to this email.

Along with the minor code changes, I've tried to clarify the behavior of
--ftp-ssl in the help/manual output.

Thanks for considering it.

-David McCreedy