Put image redirects behind $wgFileRedirects config option for now (defaulting off).

Put image redirects behind $wgFileRedirects config option for now (defaulting off).

Several issues off the top of my head:
* Redirect behavior doesn't match between the image and the page.
* Upload form doesn't appear to pick up conflicts with existing redirects; this leads to confusion when after the upload you see a page showing the already-present redirect target, but the newly uploaded file is what you get when you use the name.
* [[Image:]] link to a redirect to a non-image page links to Special:Upload with the redirect name; [[Image:]] link to a redirect to a non-existent image page just links to the redirect page... behavior seems very hard to predict.
* Caching issues; pages using the redirected image don't appear to get invalidated when the redirect page is deleted
* Upload permissions can't be matched easily to creating-redirect permissions, which may be an issue (eg, create a billion redirects to Image:Goatse.jpg with innocent names)