treewide: introduce UID_INVALID (and friends) as macro for (uid_t) -1

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
cgroup-util: Don't send SIGCONT after SIGKILL

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udevadm hwdb: discard extra leading whitespaces in hwdb

Currently a property in the form of
  FOO=bar
is stored as " FOO=bar", i.e. the property name contains a leading space.
That's quite hard to spot.

This patch discards all extra whitespaces but the first one which is required
by libudev's hwdb_add_property.

[zj: modify the check a bit]

https://bugs.freedesktop.org/show_bug.cgi?id=82311

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udev: rules - modernise add_rule a bit

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udev: rules - print the first invalid character

The current code would print the character following the first invalid
character.

Given an udev rules-file without a trailing newline we would otherwise print
garbage:

  invalid key/value pair in file /usr/lib/udev/rules.d/40-usb-media-players.rules
  on line 26, starting at character 25 ('m')

This is now changed to print

  invalid key/value pair in file /usr/lib/udev/rules.d/40-usb-media-players.rules
  on line 26, starting at character 25 ('')

(still not very good as printing \0 just gives the empty string)

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>