IPv6 support for HTTP realip module

[anaconda]

The attached patch, based on r4232, implements IPv6 support for the realip HTTP module (set_real_ip_from).

[Ruslan Ermilov]

In [4625/nginx]:

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;

[Maxim Dounin]

In [4669/nginx]:

Merge of r4614, r4624-r4629, r4631: proxy recursive changes.

*) Added IPv6 and UNIX-domain socket support in "debug_connection"

directive.

*) New function ngx_http_get_forwarded_addr() to look up real client

address.

On input it takes an original address, string in the X-Forwarded-For format
and its length, list of trusted proxies, and a flag indicating to perform
the recursive search. On output it returns NGX_OK and the "deepest" valid
address in a chain, or NGX_DECLINED. It supports AF_INET and AF_INET6.
Additionally, original address and/or proxy may be specified as AF_UNIX.

*) 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;

*) 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.

*) 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;