Repeat a query with some interval to aggregate output

Add a way to repeat a query multiple times and aggregate the output. Can use this to track statistics over time. For instance:

REPEAT -n10 -i1000 SELECT NOW(), COUNT(*) FROM foo;

Will run the query 10 times with 1000ms interval. Any produced rows should be send in the same containing result set so the presenter and dest can render it as one single result set, e.g.

+-------------+----------------+
+ Date + Count +
+-------------+----------------+
+2009-..01 + 123 +
+2009-..02 + 125 +
...

and so on.

An example usage would also be to send the final result to a chart so you can see a diagram over time of the statistics you've observed.