realip: chains of trusted proxies and IPv6 support.

realip: chains of trusted proxies and IPv6 support.

The module now supports recursive search of client address through
the chain of trusted proxies, controlled by the "real_ip_recursive"
directive (closes #2).  It also gets full IPv6 support (closes #44)
and canonical value of the $client_addr variable on address change.

Example:
    real_ip_header X-Forwarded-For;
    set_real_ip_from 127.0.0.0/8;
    set_real_ip_from ::1;
    set_real_ip_from unix:;
    real_ip_recursive on;