Bump minimum OpenSSL version to 0.9.8

OpenSSL 0.9.7 and older are considered obsolete (see
http://www.openssl.org/news/news.html). This patch updates configure.ac to
require OpenSSL 0.9.8 or newer, and removes a number of #ifdefs that are
now no longer needed.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1395582781-27966-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8392
Signed-off-by: Gert Doering <gert@greenie.muc.de>