Regression Bug
1. Navigate to 'Administration > Content' in the dockbar.
2. Select 'Documents and Media'
3. Add a text document.
4. Edit the document, changing the file to another text document.
5. Select the file.
6. In version history, checkmark the original file and the edited file.
7. Compare the files.
Expected Result: The difference between the two text files would be displayed as it currently does with 6.2.x.
Actual Result: An error page is returned.
