What's the thinking behind moving `{{ MEDIA_URL }}` outside of the block for the favicon? To be more consistent with the implementation of `page_image`, I'm guessing?

I'm a bit torn on this. On the one hand, it seems nice to have these `head/meta` images implemented the same way. On the other hand, everywhere else on the site, images need to be wrapped in the `media()` helper.

I understand we need an exception for `page_image` due to Faceboook's limitations, but I'm not sure we should change `page_favicon` as well. My vote would be to keep `page_favicon` consistent with the rest of the site - requiring the template developer to use the `media()` helper as normal. We should also add a comment to `base.html` and `base-resp.html` noting that `page_image` should *not* include the `media()` helper when implemented in individual templates.

@alexgibson, @sgarrity, @pmclanahan, @craigcook, @jgmize - thoughts?