Fix bug that incorrectly refuses oid representation eku's in polar builds

The return value of x509_get_numeric_string() was interpreted incorrectly
by ssl_verify_polarssl.c's x509_verify_cert_eku(). This patch enables the
usage of oid represenation in --remote-cert-eku options.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: David Sommerseth <dazo@users.sourceforge.net>
Message-Id: <1398415277-6880-1-git-send-email-steffan.karger@fox-it.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8627
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit e238b806f5f3843b80d5b1b2b269679210faa7f6)