Add another element to the texture tuple with a mask for the lighting.

Make needed changes in textures.py.

Because some textures have garbage in the alpha channel, this new method has some problems.

src/rendermodes.h

@@ -56,7 +56,7 @@ struct _RenderModeInterface {
     /* returns non-zero to skip rendering this block */
     int (*occluded)(void *, RenderState *);
     /* last two arguments are img and mask, from texture lookup */
-    void (*draw)(void *, RenderState *, PyObject *, PyObject *);
+    void (*draw)(void *, RenderState *, PyObject *, PyObject *, PyObject *);
 };
 
 /* figures out the render mode to use from the given ChunkRenderer */