Added JOCKEY and CHUNK_GEN SpawnReasons.

src/main/java/org/bukkit/event/entity/CreatureSpawnEvent.java

@@ -80,6 +80,14 @@ public class CreatureSpawnEvent extends EntityEvent implements Cancellable {
          * When something spawns from natural means
          */
         NATURAL,
+        /**
+         * When an entity spawns as a jockey of another entity (mostly spider jockeys)
+         */
+        JOCKEY,
+        /**
+         * When a creature spawns due to chunk generation
+         */
+        CHUNK_GEN,
         /**
          * When a creature spawns from a spawner
          */