Width of the diff table

It often happens that the diff table will be so big that it overlaps with the right sidebar.

Solution:
1. Give the td elements classes such as "label", "before", "arrow" and "after", so they are easier to target with CSS.
2. Allow linebreaks for text fields, OR give them a horizontal scrollbar.

The first step should be done in any case, so people can do their own stuff with CSS.