According to `info Damage', blast radius is multiplied
by 2/3 for groundburst and 3/2 for airburst.
Let b be the blast radius.
nukedamage() uses blast radius b for groundburst and
b*1.5 for airburst.
It's caller detonate() uses blast radius b*2/3 for
groundburst and b for airburst.
Together, this yields blast radius b*2/3 for
groundburst and b for airburst, which does not match
the documentation for airburst.
Currently, this error has no effect, because damage
drops to zero long before reaching radius b. See also
bug#724511.