Merge: Benitlux & sqlite3: fix closing SQLite statements and malformed superstring

Fix statements that were left open and did not remove the lock on the database. It now relies on iterators to close the statement after the end of the loop. This requires to actually complete the loop and not return before it is complete. A shortcut is to use `statement.iterator.to_a` when the result is expected to be short, like with a single row.

Note that I did not use `with` because it has the same problem with a `return` skipping the call to `finish`. Neither did I use `Finalizable` because it is invoked by the GC which may be much later.

Also fix one malformed superstring and improve the style of another one.

Pull-Request: #2009
Reviewed-by: Jean Privat <jean@pryen.org>