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>