heifload autorotate is now always on, and we always delete EXIF
orientation tags. If a HEIC image fails to rotate upright, at least it's
someone else's fault.
see https://github.com/libvips/libvips/pull/1680
- Add 'scratch' field to gif that holds temporary 'scratch buffer' used for rendering frames
- For DISPOSE_BACKGROUND: Set background color to transparent instead of 0
- For DISPOSE_BACKGROUND: Write background pixels into scratch after rendering current frame, so it will be used in next frame
- For DISPOSE_PREVIOUS: Save frames that are not disposed into 'previous' field in gif, when DISPOSE_PREVIOUS is specified start with that previous frame. see http://webreference.com/content/studio/disposal.html
- Add "ANIMEXTS1.0" to Application Extension parser
- Graphic Control Extension parser refactor
- Compare file contents to expected images for animated gifs in foreign tests
