Xpra: Ticket #1989: make it easier to enable mdns on win32

Now that the GUI is more prominent (#1762), users are more likely to use xpra mdns-gui to browse for sessions. This works well on all platforms we package for except on win32. We cannot bundle bonjour for windows (non-free license), but we can at least tell the user that support is missing and give them a link to the download page.

Tue, 16 Oct 2018 14:01:45 GMT - totaamwin32: status changed; resolution set

Done in r20692.

Sat, 23 Jan 2021 05:39:10 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1989