If the plugin runs at the end, and you are deleting a Site, the deletion
will not run completely because the trigger file still exists

We want to avoid deadlock situations and right now if there is a process
running with the same PID that is not our process (e.g. after a reboot)
we might be waiting forever to run the cron again. So to make this
transparent to the user, we at least post a warning into the logfile.

Preserve body structure in send_notification_email