Nameserver probes can give strange results
We should not actually retry nameserver probes, nor should we ever reattach them to a new nameserver after clear and resume.
Fortunately, the worst that happens here now is that we erroneously mark a down nameserver as up, retry it, fail, and mark it down again. Still, that's pretty ugly.
[Automatically added by flyspray2trac: Operating System: All]