High: pacemakerd vs. IPC/procfs confused deputy authenticity issue (0/4)

[0/4: make crm_pid_active more precise as to when detections fail]

It would be bad if the function claimed the process is not active
when the only obstacle in the detection process was that none of the
detection methods worked for a plain lack of permissions to apply
them. Also, do some other minor cleanup of the function and add its
documentation. As an additional measure, log spamming is kept at
minimum for repeated queries about the same PID.