bus: update kdbus.h (ABI break)

We changed creds to u32, so fix systemd sd-bus to acknowledge that.
update TODO
update TODO
sd-bus: given that the kernel now passes the auxgroups list as 32bit array to us, no need to convert to uid_t manually

This way, we can save one allocation and avoid copying the array
unnecesarily.
update TODO
update TODO
core: reindent mount/kmod tables
sd-bus: update kdbus.h from upstream
test: add test for crash when adding a JOB_NOP
core: fix assertion failure in checking a transaction with a JOB_NOP

Several functions called from transaction_activate() need to correctly
handle the case where a JOB_NOP job is being checked against a unit's
pending job. The assumption that JOB_NOP never merges with other job
types was correct, but since the job_type_is_*() functions are
implemented using the merge lookup, they need to special-case JOB_NOP
to avoid hitting assertion failures.
core: drop now-redundant special-casing of JOB_NOP

job_type_is_conflicting(X, JOB_NOP) correctly gives: false.

job_type_allows_late_merge(JOB_NOP) && job_type_is_superset(X, JOB_NOP)
correctly gives: true.
core: fix check for transaction destructiveness

When checking if the transaction is destructive, we need to check if the
previously installed job is a superset of the new job (and hence the new
job will fold into the installed one without changing it), not the other
way around.
sd-bus: update peeking into receieved messages, with recent kernel change we need to FREE them after all
update TODO
core: make sure we have enough information when doing selinux decisions

Let's ask for the security relevant bits in a race-free way, and augment
the rest from /proc.
sd-bus: make sure that when we connect to the system bus we have enough creds to make security decisions
bus-policy: steal a test case for prefix ownership from dbus1, and make sure it passes with the bus proxy enforcement
bus-policy: also add in other bus policy tests from dbus1

dbus1 only checks if these files parse correctly so let's do the same for now.
bus-policy: actually test messages against the newly added test.conf
manager: log some fatal errors at emergency level

This adds a new log_emergency() function, which is equivalent to
log_error() for non-PID-1, and logs at the highest priority for PID 1.
Some messages which occur before freezing are converted to use it.