Throw meaningful errors when SQL extraction query is invalid about deepdive HOT 5 CLOSED

This is part of a widespread issue: DD errors are impossible to parse for whoever is not familiar with the code.

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@zifeishan : Anything we can do about this?

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I think in general the error message is informative of what's happening. Can anyone give some examples where error message doesn't make sense?

I guess there are some improvements:

1. sanity check on config,
2. reduce debug output and make info-level output as default (?),
3. try to rewrite some error message

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I don't know what message we get when this happens, so I trust you.
Suggestion 1. is quite important for usability in my opinion.
I don't agree about 2.
For 3, it depends, we should pay attention to the messages we get and think if a "normal" user would understand them.

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This is perhaps done by #251, which runs with flag psql -v ON_ERROR_STOP=1.

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