avoid using XML() when displaying diffs. for diff lines, tabs are still expanded, but the resulting spaces are now turned into the UTF-8 encoding for \u00a0, which is unicode's non-breaking space. in theory, this should be just as good as using ' '. works in camino (and therefore probably all mozilla-based browsers) -- fingers crossed.
turns out XML() is extremely slow in kid, and may be responsible for the slowness of the revision page.