Can you please add sorting icons (with links to make the buttons) after the title in each column that look like:

http://moodle.org/pix/t/move.gif - for all columns that are currently not the sorted one.

http://moodle.org/pix/t/down.gif - for the current sorting column, sorted ASC

http://moodle.org/pix/t/up.gif - for the current sorting column, sorted DESC