[Freeciv-Dev] (PR#3374) struct Sprite "hack" in SDL client

["Jason Short via RT" <rt@xxxxxxxxxxxxxx>]

The SDL client uses struct Sprite * basically like a void* - there is no
struct involved; the pointer just points at an SDL_Surface.

This is bad because it is not typesafe.  The correct thing is probably
to create a real Sprite structure, even if it does just have one element
(an SDL_Surface*).  However, this is not quite as easy as it seems.

jason