Fix issue #610 - odoc html-fragment not producing headings correctly
#2810
| Job | Run time |
|---|---|
| 2m 4s | |
| 2m 53s | |
| 2m 15s | |
| 7m 38s | |
| 3m 26s | |
| 2m 17s | |
| 6m 8s | |
| 3m 58s | |
| 30m 39s |