[Nice] upnp support on windows

[Tom Kaminski]

> I don't think anyone ever compiled libnice with upnp support for windows.
> but if there's a port, then that would be good, last time I checked, the windows
> port of libgupnp was non-functional and incomplete, so I never tried it.

I'll report my experience when I try libgupnp for windows.  It seems
like there are a few dependent packages that need to be complied as
well - so it may take some tweaking.

> It should lower the failure rates at
> least for those who have symmetric NATs trying to connect to other symmetric NAT
> users.

So the STUN method would not work only in the case where you have
symmetica NAT connecting to another symmetic NAT?  Does this mean that
if a user is not using a symmetic NAT, they should always be able to
establish a connection with any other user?

- Tom