display image added judge whether it's first display

1. Using FadeInBitmapDisplayer or some other anim BitmapDisplayer we use lots, we need to judge whether it's first display when loading more datas to avoid anim twice when adapter notification changed.
2. For this, I suggest to add two method in the interface BitmapDisplayer judgeFirstDisplay() and isFirstDisplay().  It's realize with the imageView setTag with uri  and compare. Before the displayers display,  it just need to do one more thing that is judgetFirstDisplay first. The two methods can let the users implements BitmapDisplayer and realized a new Displayer themselves and have nothing effect with the using habits.   
3. Anim BitmapDisplayer the universal-image-loader realized itself, like FadeInBitmapDisplayer can be better used without users to do a second modify.