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This fixes a couple of issues with libdaemon accidentally closing an fd
that didn't belong to it. In some exotic situations that might cause Avahi to
freeze during startup. It also contains changes to make sure that daemon
processes are no session or process group leaders which should guarantee that
they never can accidently pick up a controlling terminal anymore. The update
also contains quite a few build system updates which should not matter during
runtime but only during compile time. If this update is not tagged then
avahi-daemon (and other daemons using this lib) might freeze during startup.
However that is a very hard to trigger problem, so it's not super high priority
to be tagged.