Adding monitoring for (approximate) VRAM used by textures. The information is current...

Adding monitoring for (approximate) VRAM used by textures. The information is currently only used in the profiling data of the BGE.

Here is a image of it in action:
http://www.pasteall.org/pic/show.php?id=6351

What it monitors:
  * VRAM used by textures created via bf_gpu and BL_Textures

What it does not monitor:
  * VRAM used by the Blender ui
  * VRAM used by 2d filters
  * VRAM allocated by the user via KX_Scene.pre_draw and KX_Scene.pre_draw