tests: add signal receiver program

Target to kill with a check that will be written later.

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill is converting signals names correctly

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check various ways to specify kill signal

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill print pid option

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill all user processes

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
kill: add --verbose option to display what is killed

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
lib/procutils: reset errno before strtol() call

When going through /proc the last entry made readdir() to alter errno,
which made the strtol() to think something went wrong, resulting kill(1)
tests to fail when running in --parallel mode.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
lib/procutils: notice setuid() process ownership changes

Earlier the owner of a process was determined by owner of the
/proc/<pid>/stat file.  When changes user ID privileges with setuid() the
stat file ownership is not updated, that resulted kill(1) to consider
such processes where running using same uid as the present process.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>