Extend EntityCombustEvent to allow setting combustion duration.

Also extend with two new events that track the entity or block that caused
the combustion.

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

@@ -0,0 +1,24 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.block.Block;
+import org.bukkit.entity.Entity;
+
+public class EntityCombustByBlockEvent extends EntityCombustEvent {
+
+    private Block combuster;
+
+    public EntityCombustByBlockEvent(Block combuster, Entity combustee, int duration) {
+        super(combustee, duration);
+        this.combuster = combuster;
+    }
+
+    /**
+     * The combuster can be lava or a block that is on fire.
+     *
+     * WARNING: block may be null.
+     * @return the Block that set the combustee alight.
+     */
+    public Block getCombuster() {
+        return combuster;
+    }
+}