Added a simple plug-in demonstrating the v3 plug-in API.

Added a simple plug-in demonstrating the v3 plug-in API.

To build the plug-in, do ./build log_v3 in the plugin/examples directory.

This plug-in can be tested by running an OpenVPN server like this:

 # ./openvpn --plugin plugin/examples/log_v3.so --dev tun \
             --server 192.168.240.0 255.255.255.0 --ca sample-keys/ca.crt \
             --cert sample-keys/server.crt --key sample-keys/server.key \
             --dh sample-keys/dh1024.pem

The client can be started like this:

 # ./openvpn --client --remote localhost --ca sample-keys/ca.crt \
             --cert sample-keys/client.crt --key sample-keys/client.key \
             --dev tun --nobind --auth-user-pass

This plug-in will only log arguments and environment variables it receives
during all the different plug-in phases OpenVPN currently supports.  It will
also parse the X509 certificate information given during the TLS_VERIFY phase.

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
Acked-by: James Yonan <james@openvpn.net>