Let's move things closer to journald's configuration settings, which
knows Compress= already, as a boolean. This makes things more uniform,
but also gives us more freedom to possibly swap out the used compression
algorithm one day.
This sounds overly low-level and implementation-detaily. Let's just
use the default level XZ suggests. This gives us more room to possibly
swap out the compression algorithm used, as the compression level range
will not leak into user configuration.
When disk space taken up by coredumps grows beyond a configured limit
start removing the oldest coredump of the user with the most coredumps,
until we get below the limit again.
Karel Zak
Jan Engelhardt
Lennart Poettering
Zbigniew Jędrzejewski-Szmek