don't have an interface index that's the same as the if_msghdr
interface index.
This prevents the occasional perror("SIOCGIFFLAGS") from appearing
at boot time.
While I'm there:
Make a couple of error messages more useful.
Add a missing include.
Add some braces to silence gccs dumb complaints.
Add some consts
Ansify decls
Add copyright to pmap_check.h (well, you could say it's been rewritten)
