Removed the extra surface in GLTexture. Now there are copies of the texture data in their original format (so engine can get the original data when lockScreen or grabOverlay is called). This copies will be updated when the engine calls a function that modifies the game screen/overlay, and the textures will be marked as dirty. When updating screen, the textures will be updated from the copies data if they are dirty.
svn-id: r51234
