replace "ps --pid $kpid" with "ps -p $kpid" to be posix-compliant

BSD `ps` does not support `--pid` option so switch to posix-compliant

(i do not know if there is a requirement to support any non-posix `ps`, but all `ps` I've looked at support `-p`)

see also:  http://stackoverflow.com/questions/905242/how-to-do-a-search-for-pid-bash