No boolean operator tests because the parser doesn't currently allow it.
I am currently keeping the code that performs this for now until we
decide whether to allow boolean operators inside of a select clause. It
would be easy to have the new query engine do something like this:
SELECT mean(value) < 10 FROM cpu GROUP BY time(1m)
And then you would have it return true or false for each interval, but
the same can be done through a where clause too.