#151 Happy Eyeballs / RFC 8305 support

[rustyx]

Modern browsers and utilities like curl support Happy Eyeballs - it starts a connection over IPv6, and if it hasn't succeeded within ~250 ms, starts a second attempt over IPv4 in parallel, then uses whichever connects first. This effectively hides IPv6 connectivity issues without a noticeable delay as perceived by the user.
privoxy doesn't have this feature. Consequently, when IPv6 has connectivity issues, the request appears "stuck" for a long time. This makes some users question privoxy's quality since the browser appears to "start working when I disable the proxy" when in fact the user has bad IPv6 connectivity.
Hence hereby a request to add Happy Eyeballs support to privoxy.

[rustyx]

Attaching the patch.
Also, the changes can be seen here: https://github.com/rustyx/privoxy/pull/1/changes

[Fabian Keil]

Thanks a lot for the patch.

I intend to review and test it in a couple of days.