TLS has been disabled
For some reason, in the refactoring, the SSLv23_METHOD has changed to being an SSLV3_METHOD.
The former allows (and tries to get) TLS. The latter won't.
Changing this to SSLv23 will allow either SSLv3 or TLS to work, giving you the maximum compatibility that 10942 refers to.
Disabling SSLv2 also allows TLS based compression to work.
Incidentally, disabling TLS makes Gajim non-conformant to the RFC, and therefore not an XMPP client, currently. Whoops.