Added support for TLS Application Layer Protocol Negotiation (ALPN)

This patch adds support for ALPN, based on draft-ietf-tls-applayerprotoneg-04.
It adds the new keywords 'ALPNtable' and 'prefer'. The latter accepts the
values 'sni' or 'alpn'.

Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>