geo: chains of trusted proxies and partial IPv6 support.

geo: chains of trusted proxies and partial IPv6 support.

The module now supports recursive search of client address through
the chain of trusted proxies, controlled by the "proxy_recursive"
directive in the "geo" block.  It also gets partial IPv6 support:
now proxies may be specified with IPv6 addresses.

Example:
    geo $test {
        ...
        proxy 127.0.0.1;
        proxy ::1;
        proxy_recursive;
    }

There's also a slight change in behavior.  When original client
address (as specified by the "geo" directive) is one of the
trusted proxies, and the value of the X-Forwarded-For request
header cannot not be parsed as a valid address, an original client
address will be used for lookup.  Previously, 255.255.255.255 was
used in this case.