Large course won't backup due to POST limit

BEFORE TESTING: 0a. If you don't already have one, create a SIZE_S and a SIZE_L course using the admin tool from MDL-38197 . The SIZE_L course has 1,000 activities, which is enough to demonstrate this problem. The SIZE_S course first comfortably within the default max_input_vars limit. TESTING: 1. Go to the SIZE_L course and choose Backup. 2. Click Next. 3. The next screen contains over 2,000 checkboxes. Scroll down to the end of the page (around topic 500). 4. Make a note of the last three page numbers as A, B, and C. For example, A = Page 492, B = Page 9, C = Page 606. 5. For page B, turn off user data (right checkbox). 6. For page A, turn off the entire activity (left checkbox). 7. Click Next. EXPECTED: When you click Next while waiting for the page to load, you might notice that all the checkboxes are greyed out; that indicates this change is working. 7b. Scroll down to the bottom of the review screen. EXPECTED: All activities and topics should show a green tickbox against the content and for user data, except for page B which should show an X next to user data, and page A which should show an X next to both the activity and user data. (At this point we do NOT continue with the backup; it is expected that the backup will NOT complete unless MDL-38190 and MDL-41146 have been applied. Test step numbers 8 to 11 are not used. We will do a full backup/restore of the smaller course instead, which follows.) 12. Go to the SIZE_S course and choose Backup. 13. Click Next, then Next again. EXPECTED: This time, while the page loads, the checkboxes are not greyed out. This indicates that the change is not operating because the course is well within the max_input_vars limit, meaning that backup can continue to operate without requiring JavaScript. 14. Continue through the backup process until it completes. 15. Restore the backup as a new course and continue through process. 16. Verify that course restore completes without error.