Better performance from "Rush" (by using SDL_gfx rotozoom)

Applying patch from Pere.  ALSO, bumping Tux Paint Magic Tool API version.

src/tp_magic_api.h.in

@@ -148,6 +148,11 @@ typedef struct magic_api_t {
      'w' and 'h' elements to confirm the actual size) */
   SDL_Surface * (*scale)(SDL_Surface *, int, int, int);
 
+  /* Returns a new surface containing the rotated/scaled contents of
+     an input surface, rotated to r degrees, scaled to the w dimension and keeping its aspect ratio. */
+
+  SDL_Surface * (*rotate_scale)(SDL_Surface *, int, int);
+
   /* Returns whether a particular position of the canvas has been labeled
      as 'touched,' since the mouse was first clicked; this function ALSO
      assigns the position as touched, until the next time the mouse is