When tls-version-min is unspecified, revert to original versioning approach.

For OpenSSL, this means to use TLSv1_(client|server)_method rather
than SSLv23_(client|server)_method combined with SSL_OP_NO_x flags
for specific TLS versions to disable.

For PolarSSL, this means to implicitly control the TLS version via allowed
ciphersuites.

Point out off-by-default-now setting in the openvpn(8) man page.

This patch is only included in the release/2.3 branch, because it's a
stopgap measure.  2.4 will have it on-by-default, when the remaining
handshake problems are fully debugged and solved.

Signed-off-by: James Yonan <james@openvpn.net>
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: James Yonan <james@openvpn.net>
Message-Id: <535EC5FE.6060302@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8665
Signed-off-by: Gert Doering <gert@greenie.muc.de>