Please note that the smooth lightning is a bit borken on stairs/slabs. But we are working on it!
So here is the 12w39a changelog:
- Lighting system overhauled.
- Lots of blocks interact correctly with lighting now (stairs, slabs)
- Few sound tweaks
- Fixed witch being white for some
- More bugfixes & slight tweaks!
* The client now comes with both the client-side and the server-side JAR files. The file called “minecraft.jar” should be in your “.minecraft/bin” folder as usual, and the “minecraft_server.jar” file should be in a folder called “.minecraft/server”.
- Close Minecraft.
- Go to Minecraft.jar. You can find this in Windows at %appdata%/.minecraft/bin.
- Copy your Minecraft.jar file and back it up somewhere else.
- Move the newly downloaded Minecraft.jar into the /.minecraft/bin folder, replacing the old version.
- Open up Minecraft and have fun!
I would recommend backing up your old Minecraft.jar somewhere so that you can keep all of your current mods. You can do this by just copying Minecraft.jar and pasting it into another folder.
Credits: The Minecraft Team