Can't convert Minecraft Worlds made in Beta 1.2 and down.

When somebody tries to convert a minecraft world made in Beta 1.2 and under, Minecraft can't convert it to the new Anvil World Format. Instead, it will just regen a new world and not convert it at all. This is a problem in Minecraft versions that use the Anvil World Format (Minecraft 1.3, 1.4, 1.5, 1.6)