DNS thread simplification

[Hal Murray]

In case anybody is thinking about this area...

The current code has two modes, one for server lookup and another for pool 
lookup.  The difference is that a server only wants 1 address and the pool 
can use several.

We can simplify the handoff to/from the thread if it always returns all the 
IP Addresses that it finds and the server code picks one.

-- 
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