Update CraftBukkit to Minecraft 1.5.1

Conflicts:
	pom.xml
	src/main/java/net/minecraft/server/Entity.java
	src/main/java/net/minecraft/server/EntityTracker.java
Revert "add mob spawner to list of obfuscated blocks"
Removed until we figure out what is causing lag with Engine mode 2.
This reverts commit e267cd6150cc32850c18ed8b5e607876d6a1f433.