Debug output privacy

[JeremyRand]

Right now, debug mode will output a lot of private data (e.g. domains being looked up). We should clearly warn the user of this if debug mode is enabled (both by outputting a warning, and in end user documentation). We should also audit the code to make sure that no private data is leaked outside of debug mode (I wouldn't be surprised at all if we fail this test right now).

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