Made unit_drawer's fixed_t type match the rest of the fixed_t's

int32_t is the C++ standard fixed-width type, Sint32 is SDL's. The main fixed_t definition already uses the former.

src/units/drawer.hpp

@@ -25,6 +25,8 @@
 #define DRAWABLE_UNIT_H_INCLUDED
 
 #include "map/location.hpp"
+#include "utils/math.hpp"
+
 #include <map>
 #include <vector>
 
@@ -39,9 +41,6 @@ struct color_t;
 struct SDL_Rect;
 class surface;
 
-# include <SDL_types.h>
-typedef Sint32 fixed_t;
-
 class unit_drawer
 {
 public: