For local and dynamic port forwardings (i.e. the ones which listen

For local and dynamic port forwardings (i.e. the ones which listen
on a local port), the `Auto' protocol option on the Tunnels panel
should always produce a port you can connect to in _either_ of IPv4
and v6, because the aim is for the user not to have to know or care
which one they're using. This was not the case on Windows, and now
is. Also, updated the docs to give more detail on issues like this.

git-svn-id: svn://svn.tartarus.org/sgt/putty@5083 cda61777-01e9-0310-a592-d414129be87e