Another big & bad commit:

- Added some extra search functions to rbl routines
- Fix subnet_lookup()
- Reorder some syslog messages to make more sense
- daemon() is back
- Don't let scripts execute in parallel (gives race conditions, and
  anyway something MIGHT just be configured which is necessary for further
  execution of tinc itself)
- Accidently merged check_child() with execute_script().
- Small fixes