gnutls_require_mac & gnutls_require_protocols are no longer supported.
tls_require_ciphers is now parsed by gnutls_priority_init(3) as a priority
string, documentation for which is at:
- http://www.gnu.org/software/gnutls/manual/html_node/Priority-Strings.html
+ http://www.gnutls.org/manual/html_node/Priority-Strings.html
SNI support has been added to Exim's GnuTLS integration too.