The VOMS module should set a usable end-entity certificate subject variable

Experience shows that NGINX does not send the full certificate-chain to downstream applications. This complicates the task of resolving the EEC subject for proxy-certificate chains. The NGINX VOMS module should set the ssl_client_ee_s_dn' which sets the subject, in rfc2253 format, of the end-entity certificate chain. When a non-proxy chain is presented to NGINX, ssl_client_ee_s_dnis equal tossl_client_s_dn`.