[BUG] Fullscreen window returns the wrong size details

[andre-d]

The code in Display.java has a couple lines like:

      if (Display.isFullscreen()) {
         return Display.getDisplayMode().getWidth();
      }

This is a false assumption as things like NetWM fullscreen often do not match the displayMode size.   Bug is related to: http://lwjgl.org/forum/index.php/topic,4539.0.html