BTW, I wrote a diff proc for OpenACS a while back, but never quite cleaned it up for inclusion in OpenACS. If noone else has already finished this feature, I'll try to find a spare moment to clean it up and add it to acs-tcl.
https://openacs.org/forums/message-view?message_id=342804
Wiki RSS feeds are much more useful as a diff than as full text or changelog descriptions.