Comment 4 for bug 168261

Frankly, we want to have SVG working in list-style-image, background-image, etc,
etc, not just in <img>.

So either all images work the same way (and all these places use the image
apis), or we don't support SVG images (just SVG documents) or we hack every
single one of these places somehow, probably implementing the equivalent of
SVG-to-nsIImage glue in 3-4 places.

This is complicated by the fact that for <img> we won't know we're dealing with
SVG until we get it.... For <object>, if it claims to be SVG and comes out HTML
we just render the HTML, but for <img> that would seem to be somewhat
undesirable. 404 pages in <img> tags, anyone? ;)