User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9) Gecko/20020401
Yes XDelta appears to be the perfect tool. I read part of the author's
thesis about it and it appears to be more or less an rsync style diff
for arbitrary files including binaries.
And XDelta comes with Skipjack/7.3 as well.
-Mike