geoip: trusted proxies support and partial IPv6 support.

geoip: trusted proxies support and partial IPv6 support.

The module now supports recursive search of client address through the
chain of trusted proxies (closes #100), in the same scope as the geo
module.  Proxies are listed by the "geoip_proxy" directive, recursive
search is enabled by the "geoip_proxy_recursive" directive.  IPv6 is
partially supported: proxies may be specified with IPv6 addresses.

Example:
    geoip_country .../GeoIP.dat;
    geoip_proxy 127.0.0.1;
    geoip_proxy ::1;
    geoip_proxy 10.0.0.0/8;
    geoip_proxy_recursive on;