Course completion uses cache inefficiently

Note: This test is just a quick one to exercise the completion cache a little and make sure we didn't break it. It already passed before the change, as well as after. 1. Enable completion tracking (for server and a test course). 2. On a course, create a Page object. Under completion options, set it so that students can manually mark it complete. 3. Create a second Page object. Set this one so it is automatically marked complete when viewed. (Use 'save and return to course' so as not to view it yet) 4. Turn editing off. EXPECTED: Both checkboxes should be visible but not ticked. 5. Tick the checkbox next to the first Page. EXPECTED: The checkbox appears ticked. 6. Reload the page. EXPECTED: The checkbox still appears ticked. 7. Click into the second Page, then click back to the course page. EXPECTED: Both checkboxes are now ticked.