Chas Emerick wrote this.  Go here http://snowtide.com/jsdifflib for more
information.

Its a javascript diff library based on Python's SequenceMatcher.

I've updated the js code to avoid "for...in" so that this library is compatible
with protoype, http://www.prototypejs.org/.  Check out
http://www.prototypejs.org/api/array for more information as why the "for...in"
construct is to be avoided.