Update Bukkit for Minecraft 1.5.2
Move world generator warning to CraftBukkit. Fixes BUKKIT-2565
Updated version to 1.5.2-R0.1 in pom.xml for BETA.
Updated version to 1.5.2-R0.2-SNAPSHOT for development towards next release.
Merge branch 'master' of https://github.com/Bukkit/Bukkit