bus: properly unset default bus pointer when destroying last reference
nspawn: always use default bus
nspawn: add --quiet switch for turning off any output noise
Update some message formats

Use PID_FMT/USEC_FMT/... in more places.

Also update logind error messages to print the full path to a file that
failed. This should make debugging easier for people who do not know
off the top of their head where logind stores it state.
udev: add zram to the list of devices inappropriate for symlinks

udev seems to have a race condition with swapon to see which can open
/dev/zram0 first, causing swapon to fail. Seems to be most noticeable
on arm devices one out of every 7 times or something.
core: only send SIGHUP when doing first kill, not when doing final sigkill
bash-completion: fix completion of complete verbs

When doing 'command verb<TAB>', the arguments for verb would be
proposed, but it is too early. We should complete verb first.

https://bugs.freedesktop.org/show_bug.cgi?id=74596
transaction: print more information about conflicting jobs

Also remove some debug statement that should not have been committed.