fixed blurry sprite/text when setting an anchor which results in floating point coordinates

I had an issue of blurry text when using PIXI.Text when setting its anchor to 0.5 to be centered. I've talked a bit about that on the forum: http://www.html5gamedevs.com/topic/2209-blurry-text-using-custom-font/

In my opinion, we should never use floating point to render a sprite, because this could result of blurry effect if it's not pixel perfect.