Xpra: Ticket #1889: make it easier to spot dead sockets

As per XDG Base Directory Specification: Files in this directory MAY be subjected to periodic clean-up. To ensure that your files are not removed, they should have their access time timestamp modified at least once every 6 hours of monotonic time or the 'sticky' bit should be set on the file.

Let's use this to also make dead socket probing faster: if the socket is likely to be live then it will have a recent timestamp.

Wed, 27 Jun 2018 13:00:11 GMT - Antoine Martin: owner changed

@maxmylyn: just a FYI, feel free to close.

Wed, 27 Jun 2018 16:21:23 GMT - J. Max Mena: status changed; resolution set

Sat, 23 Jan 2021 05:36:29 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1889