zsh-completion: add s-a critical-chain
zsh_completion: fix udevadm monitor flags

The brackets in the _arguments description of udevadm monitor need to be
escaped.
cgls: add --machine/-M

cg_get_machine_path is modified to include the escaped machine name
+ ".nspawn" if the machine argument is nonnull.
dbus-execute: fix introspection

Add missing property and remove duplicate properties already in
src/core/dbus-kill.h
Annotate some functions as _const_

hexchar,unhexchar,octchar,unoctchar,decchar,undecchar are
all const functions.