This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

This is a combination of 3 commits.

- Update the bare repositories info/attributes if the default branch is updated
- Check the diff attributes of a file before showing a diff
- Update CHANGELOG

Added highlight colours to diff rows

Closes #13852

Closes #14875

Closes #3769

Closes #14327

This builds on the changes introduced in
https://gitlab.com/gitlab-org/gitlab_git/merge_requests/72 and results
in merge requests with large diffs (e.g. due to them containing minified
CSS) loading much faster.

Closes #13751

Since gitlab_git 8.0, blob data are lazy-loaded so we have to call
blob.load_all_data!(repo) to eager-load them.

Fixes #13458.

* Use commit objects instead of IDs when generating diffs
* Use proper references when generating MR's source and target
* Update broken specs

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Now we apply syntax highlighting to the whole old and new files.
This basically help us to highlight adequately multiline content.