Quiz cron not closing old attempts after quiz close date

Open mod/quiz/cronlib.php and find the chunk of code that looks like

          WHERE iquiza.state IN ('inprogress', 'overdue')

            AND iquiza.timemodified >= :processfrom

            AND iquiza.timemodified < :processto

Delete the middle of those three lines, so that it looks like

          WHERE iquiza.state IN ('inprogress', 'overdue')

            AND iquiza.timemodified < :processto

If you have a small Moodle site, then you can probably do that without worrying.

If the quiz_attempts table if you Moodle site has a lot of rows, then making this change may cause cron to run unacceptably slowly. (It would be useful to know how slow it is, if anyone tries it on a big site.)

Really, we need to re-run QA tests MDLQA-4166 to MDLQA-4177, or at least the parts of them that involve cron.

Testing instructions for the initial problem:
1. Create a quiz with a close date enough in the future to run steps 2 and 3 first. Set the quiz to automatically submit attempts when time expires.
2. Attempt the quiz as a student, but don't finish the attempt.
3. Run the moodle cron.
4. Verify that the student attempt hasn't been closed.
5. Wait long enough that the quiz has been closed for at least quiz mingraceperiod (60 secs by default), and run the moodle cron again.
6. Verify that the student attempt has closed. (Note: this check should be done as the instructor, since the student viewing his own attempt will close it on view.)

(To replicate the problem in current moodle, note that the overdue attempt processor only runs a maximum of once an hour. This patch eliminates the need for that delay, as well as fixes the bug.)