openssl: add more descriptive message for 'no shared cipher' error

openssl: add more descriptive message for 'no shared cipher' error

Overzealous users using the --tls-cipher option, or users with actual
incompatible crypto libaries often waste quite some time debugging the
'no shared cipher' error from openssl. See e.g. trac ticket #359:
https://community.openvpn.net/openvpn/ticket/359

This change adds a more clear, verb 1 error message reporting the problem
directly to the user, instead of just printing the openssl error.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <544EB12E.40200@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9209
Signed-off-by: Gert Doering <gert@greenie.muc.de>