Visual diffs/2008 project

Visual Diff was a Google Summer of Code 2008 project by guyvdb and mentored by Brion. It can be enabled by setting $wgEnableHtmlDiff to true. As a side project the basic diff algorithm was optimized (available by setting $wgExternalDiffEngine to 'wikidiff3').

Prospects
There are still a number of enhancements needed:
 * A fallback mechanism for extremely long computations
 * A better GUI on the client side
 * Better tooltip windows that are valid XHTML.
 * Support for jumping to the first change in a page.
 * Better i18n. This was a big issue last summer.

Abstract
The goal of the project is to extend and improve the current diff page to render the changes instead of showing the source diff. The resulting "parsed inline diff" would be very easy to use. The algorithm that will achieve this is based on the HTML diffing library used in DaisyCMS.

Code
Work started out in the visual_diff branch which was merged with trunk later on. The branch is now obsolete.

HTMLDiff was removed from core in r58267; see also bug #19859,