This introduces a new data threshold setting for sd_journal objects
which controls the maximum size of objects to decompress. This is
relieves the library from having to decompress full data objects even
if a client program is only interested in the initial part of them.
This speeds up "systemd-coredumpctl" drastically when invoked without
parameters.
'systemd-coredumpctl' will list available coredumps:
PID UID GID sig exe
32452 500 500 11 /home/zbyszek/systemd/build/journalctl
32666 500 500 11 /usr/lib64/valgrind/memcheck-amd64-linux
...
'systemd-coredumpctl dump PID' will write the coredump
to specified file or stdout.