multiple instances of the same function confuses CQ output

[beckettsean]

From #3469 (comment).

A CQ like SELECT MEAN(value1), MEAN(value2) FROM... writes a single column to the result series, called mean. If an AS alias is used both values are successfully written.

We could throw a parser error when multiple identical functions are used without an explicit alias, or we could write the values into the new series as mean_value1, mean_value2. Not sure if there are other fixes that make sense.

[jwilder]

Fixed via #5742