Prior plugin version returns wrong results. I'm not sure why.
This commit fix the bug however it reduce functionality since
there is no way now to include/exclude certain users.
- Fix USERS=ALL only enumerating processes with a tty or pty attached
(and thus not eg. user-owned FastCGI processes, owned by eg. Apache)
- ps(1) is used to make process list parsing easier and more robust
- OTHERS_FIELD now defaults to disabled