core: don't allow enabling if unit is masked
man: mention docker as type of virtualization
NEWS: update for 217
unit: move UnitDependency to unit-name
systemctl: add add-wants and add-requires verbs
note on relative symlink in os-release
nspawn: copy /dev/net/tun from host

This enables tuntap support in the container (assumning the necessary capabilities are in place).
sd-bus: sync kdbus.h (ABI break)

Sync kdbus.h once again. Two thing have changed:

 a) KDBUS_CMD_EP_* was renamed to KDBUS_CMD_ENDPOINT_*
 b) struct kdbus_cmd_hello and struct kdbus_cmd_make gained a
    'features' bitfield (which is currently unused)
Update TODO
core: map the 'rescue' argument to rescue.target

Even though the 'emergency' and 'single' aliases come from sysvinit, the
lack of 'rescue' is still quite confusing (caught me by surprise for the
9th time yet) and inconsistent with `systemctl rescue` as well.
time: functions named "internal" really shouldn't be exported

Also, let's try to make function names descriptive, instead of using
bools for flags.
util: avoid double close of fd

We could end with a double close if we close the fd loop and flush_fd
fails. That would make us goto fail and there we close the fd once
again. This patch sets the fd to the return value for safe_close: -1
A fd with negative value will be ignored by the next call to
safe_close.

CID#996223
man/systemctl: document enable on masked units
sd-event: be more careful when enabling/disabling signals

When a child event is disabled (in order to be freed) and there is no
SIGCHLD signal event, sd_event_source_set_enabled will disable SIGCHLD
even if there are other child events.

Also remove some unneeded signalfd updates.

https://bugs.freedesktop.org/show_bug.cgi?id=84659

Based-on-a-patch-by: Hristo Venev <mustrumr97@gmail.com>
sd-event: also update signal mask when disconnecting sources
update TODO
systemctl: suggest -xe not -xn

https://bugzilla.redhat.com/show_bug.cgi?id=1150289
sd-bus: check return value of asprintf()

Check for OOM conditions of asprintf() in bus_set_address_user().
man: SyslogIdentifier= has an effect on journal logging too
logind: mount per-user tmpfs with 'smackfsroot=*' for smack enabled systems