KNOWN BUGS:

20061101
- IPv6 untested and might not work at all.

20061016
- Scanning in-addr.arpa for PTR records to add sshfp records is missing.

20061004
- using opts.append(x) does not work, as x is never appended to the current
  loop. This means the whole option processing needs to become re-entrant
  after fixing an argument. yuck.

20060927
- sshfp -a xelerance.com -o 1 @ns1.xelerance.com gives:
  AXFR error: ns1.xelerance.com No permission or not authorative for  xelerance.com -o 1 ; aborting
  workaround for now: return usage() and let them change order of arguments. 
- Running sshfp against the same nameserver twice using -a @ns0 gives different output all the
  time. Looks like ssh-keyscan is sensitive to failures.

20060921:
- if a zone contains non-working glue A records, then ssh-keyscan aborts. Bug reported upstream

FEATURE reqeust:
- some mode (-V) that verifies all keys in knownhosts file and compares them with a scan
