Allow auth_ldap in NGX_HTTP_LIF_CONF context.

[sobolev-es]

Сonfiguration example

geo $authentication {
    default "on";
    127.0.0.1 "off";
    192.168.0.0/24 "off";
...
}

server {
...
location / {
    if ($authentication = "on"){
       auth_ldap "UCS Auth required!";
    }
    auth_ldap_servers ucs;
...
}

[sobolev-es]

Related issue #77