add API for plug-ins to write to openvpn log

add API for plug-ins to write to openvpn log

Some plugins want to add messages to the openvpn log file. The
plugin_log() and plugin_vlog() APIs provide ways for them to do so.

OPENVPN_PLUGINv3_STRUCTVER is not incremented as the v3 plugin API
is new in 2.3 and this is merged during alpha phase.

Signed-off-by: Heiko Hund <heiko.hund@sophos.com>
Acked-by: David Sommerseth <davids@redhat.com>
Message-Id: 1343920822-29161-1-git-send-email-heiko.hund@sophos.com
URL: http://article.gmane.org/gmane.network.openvpn.devel/6946
Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>