sshttp IPv6 trickery

During last hackweek, I added IPv6 support to
sshttp. Courtesy of IPV6_TRANSPARENT in recent Linux
kernels, it works as you know it from IPv4.

Beside that, it's now also possible to add IPv6 backends
to the frontend reverse proxy which is part of lophttpd,
and to run it on an IPV6 address to the outside.