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/entity/Projectile.java

@@ -25,6 +25,8 @@ public interface Projectile extends Entity {
     /**
      * Determine if this projectile should bounce or not when it hits.
      *
+     * If a small fireball does not bounce it will set the target on fire.
+     *
      * @return true if it should bounce.
      */
     public boolean doesBounce();