This update fixes world generation bugs that would appear in 1.7. It is recommended that you use this version and load up important areas of your world before heading into Minecraft 1.7."
Aaahhhh right, interesting indeed..
its inportant to go trho all the generated eryas with 1.4.6 before you update to 1.7 becouse it moves the files that store struktures from th biomes files that are gona get tjanged to a seperet file. if whe dont update all the struktures is gana get distroyd or not work. that whil say that there whoudent spawn whithes or witherskellitons