New JPEG settings:

 - Use Lanczos everywhere (Mitchell really isn't that good for mipmap scaling)
 - Use 1x1 subsampling everywhere (the discoloration just isn't worth it)
 - Tone down to quality 87 to get the file sizes back down to almost-normal level.

Mainly tuned for fullscreen viewing (I haven't looked at thumbnails). About 8%
increased file size, it seems.