Introduce an option to resolve dns names in advance for --remote, --local and --http...

Introduce an option to resolve dns names in advance for --remote, --local and --http-proxy

Also introduce x_gc_addspeical function that allows to add objects with a
custom free function to the gc.

Some additional addrinfo cleanup

Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1395576786-17507-1-git-send-email-arne@rfc2549.org>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8386

Signed-off-by: Gert Doering <gert@greenie.muc.de>