Currently, a checked out PR shows diffs between the base branch and your git working tree (basically your files on disk). We should offer a way to change this diff to be between the base branch and the remote head branch of the PR.

Some implications:

• This would mean that right side of the diff, which is currently editable, would be read only (at least when this is different from the file on disk).
• This might cause problems with the quick diff (investigation needed).

@hediet FYI and thanks for continuously providing feedback!