util: make use of the new getrandom() syscall if it is available when needing entropy

Doesn't require an fd, and could be a bit faster, so let's make use of
it, if it is available.
missing: simplify memfd ifdeffery
update TODO
missing: no tabs please, we are british
sd-bus: properly handle removals of non-existing matches
nspawn: ignore EEXIST when creating mount point

A combination of commits f3c80515c and 79d80fc14 cause nspawn to
silently fail with a commandline such as:

  # systemd-nspawn -D /build/extra-x86_64 --bind=/usr

strace shows the culprit:

  [pid 27868] writev(2, [{"Failed to create mount point /build/extra-x86_64/usr: File exists", 82}, {"\n", 1}], 2) = 83
busctl: add new "capture" verb to record bus messages in libpcap compatible files, for dissection with wireshark
udev: path_id - update comments
missing.h: fix wrong __NR_getrandom syscall def

278 is vmsplice on x86_64. 318 is what we want:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/x86/syscalls/syscall_64.tbl
bash-completion: rework startable/restartable units once more

I tried to use 'systemctl --all list-units' to filter unit files, but
this always filters out unit files which are not loaded. We want to complete
systemctl start with those units too, so this approach is not going to work.

New version is rather slow, but hopefully correct.
systemctl: let list-{units,unit-files } honour --type

The docs don't clarify what is expected, but I don't see any reason
why --type should be ignored.

Also restucture the compund conditions into separate clauses for
easier reading.
systemctl: obey --state in list-unit-files
bash-completion: use improved filtering to make things faster
zsh-completion: update start/restart completions

Now zsh should behave the same for those two subcommands as bash.
keymap: Ignore brightness keys on Dell Inspiron 1520 to avoid double events

On the Dell Inspiron 1520 both the atkbd and acpi-video input devices report
an event for pressing the brightness up / down key-combos, resulting in user
space seeing double events and increasing / decreasing the brightness 2 steps
for each keypress.

This hwdb snippet suppresses the atkbd events, making the Inspiron 1520 work
like most modern laptops which emit brightness up / down events through
acpi-video only.

Reported by Pavel Malyshev <p.malishev@gmail.com>

https://bugzilla.redhat.com/show_bug.cgi?id=1141525
sysusers: Preserve ownership and mode on /etc/passwd and friends

When running sysusers we would clobber file ownership and permissions
on the files /etc/passwd, /etc/group and /etc/[g]shadow.

This simply preserves the ownership and mode if existing files are
found.
util: don't block on getrandom()
util: unify how we see srand()
memfd: always create our memfds with CLOEXEC set

We really shouldn't create fds ever that have the flag unset.
CODING_STYLE: clarify that we really should use O_CLOEXEC everywhere