I just tried latexdiff, and it choked on either xypic or pb-diagram
code. And I don't think Tim's wdiff trick will handle changes like
\begin{foo}
Stays the same.
\end{foo}
changing to
\begin{bar}
Stays the same.
\end{bar}
since it will put braces around the \begin{...} commands which
will mess up the nesting.
Are there any other options people know of? What about something
that compares dvi or pdf files??
Dan