From the change description view, there's a big button that says "View
Diff". On the diff view, however, there is no corresponding button to back
to the change description. (I realize that I can click on the change title,
but it's less obvious, and it's asymmetric.)
Alternatively, I don't see why viewing the diff should necessarily hide the
change description. It's sometimes useful as a reference without having to
open a separate tab. It's also more similar to the output that certain
diffhtml scripts generate.
