Cannot cancel queries that are already streaming results

[carlosms]

We are cancelling queries correctly if gitbase still has not responded with the results. But when gitbase starts streaming rows, our query cancellation leaves the query running on gitbase.

For example, select * from files order by file_path can be cancelled because gitbase does not return until it finishes the ordering. But select * from files starts to collect the rows quickly, and if you cancel after a time the query continues in gitbase. The problem is this select.