Workaround missing SSL_OP_NO_TICKET in earlier OpenSSL versions

058e889d introduced using SSL_OP_NO_TICKET, leading to build failures on
systems that could build 2.3.2 fine.  Inside the 2.3 release train, we
do not want to change requirements, so for those build environments, ignore
missing SSL_OP_NO_TICKET.  2.4 will require more recent OpenSSL, though.

Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20140322183508.GZ16637@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8384

Signed-off-by: Gert Doering <gert@greenie.muc.de>