options `start' and `stop' now (unless I have forgotten any). This allows
us to call the scripts from /etc/rc.shutdown with the correct option.
The (42 or so) ports that already DTRT before are unchanged.
Suggested by: neil.long@materials.oxford.ac.uk (Neil J Long)
Add etc/rc.d/arpwatch.sh
Don't mention arp.dat as an "installed" file - we may want
this after pkg_delete.