KWSys: Use "ps -Af" for process list on QNX

In order to kill process trees we need to list all processes to find
those whose parent we are killing.  We implement process listing on QNX
using "ps -Af" and parsing the resulting format:

  UID        PID       PPID  C STIME TTY          TIME CMD
  %*d         %d         %d  %*[^\n]\n