Further improvements to plugin support:

Further improvements to plugin support:

 - Renamed struct entries to explicitly show them as disabled
 - Added a warning if USE_SSL is enabled, but neither ssl_verify_openssl.h or ssl_verify_polarssl.h is included
 - If neither of those files is included, disable ssl support for a plugin including openvpn-plugin.h

Signed-off-by: Adriaan de Jong <dejong@fox-it.com>
Acked-by: James Yonan <james@openvpn.net>
Signed-off-by: David Sommerseth <davids@redhat.com>