Besides the confusingness of the nodns argument being negatively
phrased, it had the value 0 in every existing call. Split out the nodns
special case into a separate function resolve_numeric.
This also has the side effect of changing the number of parameters to
the resolve function, which will cause a compile error for any calls I
might have missed changing when I changed the return code meaning in the
previous commit.
Ncat has its own copy of resolve, which obeys the global o.nodns rather
than a parameter. I'm leaving that alone for now. But give it the same
resolve_internal function, and make resolve call it with different flags
depending on the value of o.nodns.