Side by side view broken

Currently the side by side view for diffs is broken.

This is because the buttons calls the wrong url.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/437/diffs.json?view=parallel

should be

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/437/diffs?view=parallel

To reproduce it, open a random MR on gitlab and click the "Side-by-side" button

mentioned in issue #1241 (closed)

The URL only seems to be wrong on the first call of a MR.

Reproducable after you switch to the changes tab:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/437

Fixed if called directly:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/437/diffs

This broke in 27e75344. The exact reason for this fix is described here:

https://github.com/ZeoAlliance/gitlabhq/commit/5493e27d53d157c1d43dca6c29815f4bc3a39c5c

Let's suppose my repo is gitlab-org/gitlab-test. This is what's happening:

a. When you first go to the Merge Request page, the tabs for "Discussion", "Commits", and "Changes" are wired to JavaScript buttons.

b. Upon clicking on "Changes" for the diff, an AJAX call for this path is requested:

/gitlab-org/gitlab-test/merge_requests/6/diff.json

c. This causes MergeRequestsController to return the entire page in JSON format, including the buttons, and the page is updated directly through the JavaScript code.

It seems like the easiest solution would always make the "Inline" and "Side-by-Side" buttons show in HTML format, no matter what the original request format was.

mentioned in merge request !460 (merged)

Status changed to closed by commit 546dab6d

mentioned in commit 3302888c

mentioned in merge request !14785