Queries with a semicolon at the end fail silently

This is confusing for the user as the error message from Tableau is not meaningful. This PR fails queries with ; in them.
That makes sense, but is ultimately orthogonal. I'm not especially well versed in sequel.... but is it possible to construct a perfectly valid query that has a semicolon in it anywhere but at the end? The question is: can we, 100% of the time, determine that the presence of a semicolon means that the query is malformed, or do you need to actually parse the SQL to make that determination?

I'd gladly help hunt for such a bug, but because my internship is over I no longer have an installation of Tableau to work with. Probably worth checking the log file. Otherwise I'll be back in January.