Why does the wire-frame material fades across the object? Why does the wire-frame material fades across the object?

Here is what I did - I created a new material and I selected on "Wire" and I made it shadeless. Then, I created a new material and assigned the new material on the on the object. However, doing it that way, it allows me to render both materials - "Wire" and "Surface". Then I get a fading result like this - 


But I want all of the edges to be shown, not a fading result. How can I make that?

Here is the blend file if anybody wants to check it out - 
http://www.pasteall.org/blend/31021
Enable Z transparency and increase the Z offset: