org.docx4j.diff in svn now uses code which is in src/diffx, so you'll need to add that path in your IDE.
'ant dist' takes this into account.
Previously the diffx code was supplied in a jar, and org.eclipse.compare was in src/main/java
(I've put the diffx code in a separate directory tree, since i've made a few changes and it is useful to have under version control, and it has no dependencies on docx4j - it is useful on its own (for example, I use also it in a .NET application courtesy of IKVM) ).
there is now also a dependency on commons-lang; this is defined in the pom.