one of the tests in the resolver system test depends on dig
getting no response to its first two query attempts, and SERVFAIL
on the third after resolution times out.
using a 5-second retry timer in dig means the SERVFAIL response
could occur while dig is discarding the second query and preparing
to send the third. in this case the server's response could be
missed. shortening the retry interval to 4 seconds ensures that
dig has already sent the third query when the SERVFAIL response
arrives.
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