NEW FEATURE: FTP SSLv2 connections

[davidrg]

From the K95 bugs list:

K95 follows the specification for FTP AUTH SSL and FTP AUTH TLS and
does not support the antiquated SSLv2 protocol on FTP connections.
Unfortunately, not everyone else follows the specification. A new command

SET FTP BUG USE_SSL_V2 {ON, OFF}

has been added to allow SSLv2 to be used with servers that won't
negotiate SSLv3 or TLSv1. This is available in the next release.

The code to support this should all be present, but SSLv2 (and SSLv3) are no longer enabled by default in OpenSSL if they're even present at all. At a minimum, OpenSSL probably needs to be built with enable-ssl2 enable-ssl3 but if OpenSSL 3.x doesn't support these older protocols then we should document this feature as really being a custom build option.