networkd: fix typo

It's HAVE_SPLIT_USR not HAVE_SPLIT_USER
update TODO
util: add hexdump() call to create pretty hexdumps of data

This is very useful when debugging sd-bus to look at messages.
sd-bus: don't access invalid memory if a signal matcher was freed from its own callback
sd-bus: don't choke if somebody sends us a message with a unix fd count of 0

It's kinda pointless to include a unix fd header field in messages if it
carries the value 0, but let's do this anyway...
utmp-wtmp: allow overriding username on wall

utmp_wall() now takes an optional argument 'username_override' which
allows the caller to override the username shown on wall messages.
journald will use this to inform users that its wall messages comes from
'systemd-journald'.
journald: add support for wall forwarding

This will let journald forward logs as messages sent to all logged in
users (like wall).

Two options are added:
 * ForwardToWall (default yes)
 * MaxLevelWall (default emerg)
'ForwardToWall' is overridable by kernel command line option
'systemd.journald.forward_to_wall'.

This is used to emulate the traditional syslogd behaviour of sending
emergency messages to all logged in users.
timedated: use builtins for integer log and exp
zsh completion: Install _sd_machines with _machinectl

_machinectl uses _sd_machines to provide a list of all available
machines.
_sd_machines: Use machinectl --no-legend

Otherwise bogus entries from the header and footer would show up in the
completion list.
timedated: print delay and jitter in debug output
sd-rtnl: make RTM_NEWLINK report EEXIST by default

Use RTM_SETLINK to update an existing link.
networkd: netdev - support joining already existing netdevs
sd-rtnl: never treat broadcasts as replies

Otherwise the sequence number of a broadcast may match the sequence number of a
pending unicast message and cause confusion.
nspawn: UP the host side of the veth pair after adding it to a bridge
Use strlen even for constant strings

GCC optimizes strlen("string constant") to a constant, even with -O0.
Thus, replace patterns like sizeof("string constant")-1 with
strlen("string constant") where possible, for clarity.  In particular,
for expressions intended to add up the lengths of components going into
a string, this often makes it clearer that the expression counts the
trailing '\0' exactly once, by putting the +1 for the '\0' at the end of
the expression, rather than hidden in a sizeof in the middle of the
expression.
timedated: handle external system time changes