[UI] Missing navigation within the diff interface

[ribasushi]

Here is how a usual debugging session goes: ...

1. Go to metacpan find module within dist in question
2. Realize something changed strangely, go to the bottom left, ask for a diff with a previous version
3. Realize this shows me only one-file diff, curse, go back to the pod-page
4. Go to the dist-view (click on top)
5. Go to diff on the bottom right again, see what I wanted to see at point 3

It would be awesome if the "single file diff" had a "get full dist diff" link, so one can jump from point 2 to point 5 directly

[oalders]

We could add this link near the "This is a file diff" message. We would only need to show it for file diffs.