When you summon a saddled pig inside of a Double Stone Slab, you get it out with a carrot, and use the carrot to make it face antother direction than it was initially summoned in, then use the /entitydata command to give it NoAI, and teleport it back it the Double Stone Slab and leave the game, it will be facing in the direction it was summoned in.

Steps to recreate

1. Use the command "/summon Pig X Y Z

" and summon it inside of a Double Stone Slab.

2. Put a carrot in hotbar 1 and select hotbar 1.

3. When it is facing in another direction than it was initially summoned in, use the command "/entitydata @e[type=Pig]

4. If the pig is no longer inside of the Double Stone Slab, then use the command "/tp @e[type=Pig,c=1] X(of the Double Stone Slab) Y(of the Double Stone Slab) Z(of the Double Stone Slab)

5. Save and quit to title, then reopen the world and observe that the rotation of the pig has changed.