Snapshot 13w09a came out:
* Mobs can now ride mobs riding other mobs/vehicles.
* When a player disconnects in a minecart/on a pig/whatever, the thing the player was riding goes with them.
* Added Minimum Smooth Lighting option.
* Animated textures now have to have an animation definition (txt file).
* Added HD font support.
* Language files updated.
* Bug fixes.