Further nasty regular expression work, to patch up diff output so that it
doesn't try to self-close DIV tags. Since the system works internally with
XHTML but pages are served as if HTML to prevent browsers choking on the
unusual data type, self-closing elements are ignored - esentially the
browser views the "/>" closing the tag as a small syntax error. With DIVs,
this can lead to big problems when diffs are viewed; the diff engine
canonicalises empty DIV containers, such as those used for automatic tables
of contents and turns them into self-closing elements, which browsers then
think are still *open* when rendering the page. The result is a bit of a
mess. Anyway, replacing self-closing DIVs with normal HTML container style
syntax works around the issue.