X330: Mirror Image Binary Trees Exercise (Modified)

Given two binary trees, return true if and only if they are mirror images of each other. Note that two empty trees are considered mirror images.
Here are methods that you can use on the BinNode objects:
   interface BinNode {
      public int value();
      public void setValue(int v);
      public BinNode left();
      public BinNode right();
      public boolean isLeaf();
   }