[atlas] "Spoofing" tests.

> A concrete demonstration on the prevalence(?) of networks allowing 
> source address spoofing would help in getting this hole plugged

a jillion spoofed botnets did not make the point pretty clearly?

hypothesis: atlas probes show a bias toward clueful locations.  unless
there is a calibration set with a different, or better yet known, bias,
what useful is actually being measured?  unless it's a name and shame
game.  and then you will want to know if things 'improve' over time,
which means it is not a one-shot.

randy