Filter entity spawning sanely.

src/main/java/net/minecraft/server/World.java

@@ -882,7 +882,7 @@ public class World implements IBlockAccess {
             boolean isAnimal = entity instanceof EntityAnimal || entity instanceof EntityWaterAnimal || entity instanceof EntityGolem;
             boolean isMonster = entity instanceof EntityMonster || entity instanceof EntityGhast || entity instanceof EntitySlime;
 
-            if (spawnReason == SpawnReason.NATURAL || spawnReason == SpawnReason.CHUNK_GEN || spawnReason == SpawnReason.JOCKEY || spawnReason == SpawnReason.SPAWNER || spawnReason == SpawnReason.BED || spawnReason == SpawnReason.EGG || spawnReason == SpawnReason.VILLAGE_INVASION || spawnReason == SpawnReason.VILLAGE_DEFENSE || spawnReason == SpawnReason.BUILD_SNOWMAN || spawnReason == SpawnReason.BUILD_IRONGOLEM) {
+            if (spawnReason != SpawnReason.CUSTOM) {
                 if (isAnimal && !allowAnimals || isMonster && !allowMonsters)  {
                     entity.dead = true;
                     return false;