Memory leak switching texture packs

Switching texture packs several times eventually exhausts all available memory and crashes the game. Specifically, direct memory (as in ByteBuffer.allocateDirect), not the Java heap, fills up. This happens even without loading up a world.

To reproduce this more easily, limit the amount of memory available to Java by adding -Xmx512M -Xms512M -XX:MaxDirectMemorySize=512M to the command line.