Before a 404 would be rendered only after a request to Gitaly would
return with an InvalidArgument error. Now we check that the ref have a
valid format before sending it to Gitaly. In both cases, a 404 is
returned to the user, but this change prevents Gitaly from generating
error noise in production.
Closes https://gitlab.com/gitlab-org/gitaly/issues/1425
When a diff has a significant number of commits, the previous behavior would
attempt to render the Markdown on all the commit messages but only display
1000 of them. To avoid additional work, we only need to render the Markdown
on the set that is displayed.
