Log: services: Some extra detail about which pid is being killed
Fix: services: Remove file descriptors from mainloop as soon as we have drained them
Fix: services: Remove cancelled recurring ops from internal lists as early as possible
Fix: mainloop: Better handle the killing of processes in the act of exiting

Also ensure that calling mainloop_child_kill() with a pid not in
'child_list' does not result in the last known child being killed.