update rendering

*fix a bug in last commit, that the HP bar inner fill wont be painted in
UC browser.(since I changed it's width from 1 to 28, it works now)
*update the render quest in Scene and Actor class. when the "repaint"
flag is false, it's wont be repaint any more(until the flag turns true
again)
*update the rendering of NinePatch : add a center_render method that
only repaint the center part of a NinePatch. It would be useful when
handling rendering a showing Dialog.