https://meta.discourse.org/t/markdown-preview-and-result-differ/263878
The result of this markdown had different results in the composer preview and the post. This is solved by updating Loofah to the latest version and using html5 fragments like our user had reported. While the change was only needed in cooked_post_processor.rb for this fix, other areas also had to be updated due to various side effects.
Previously this mapping of **cooked** images was only being run for oneboxes. Now it runs for all images, so we can transform hotlinked images without needing to immediately update `raw`
On some installations, this would fail with 'index row size exceeds btree version 4 maximum'. This commit replaces the (post_id, url)` index with a `(post_id, md5(url))` index, which is much more space efficient.
This will make future changes to the 'pull hotlinked images' system easier. This commit should not introduce any functional change.
For now, the old post_custom_field data is kept in the database. This will be dropped in a future commit.
