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

src/tuxpaint.c

@@ -2289,6 +2289,7 @@ static Uint8 magic_linear_to_sRGB(float lin);
 static float magic_sRGB_to_linear(Uint8 srgb);
 static int magic_button_down(void);
 static SDL_Surface *magic_scale(SDL_Surface * surf, int w, int h, int aspect);
+static SDL_Surface *magic_rotate_scale(SDL_Surface * surf, int r, int w);
 static void reset_touched(void);
 static Uint8 magic_touched(int x, int y);
 
@@ -21836,6 +21837,7 @@ static void load_magic_plugins(void)
       magic_api_struct->canvas_w = canvas->w;
       magic_api_struct->canvas_h = canvas->h;
       magic_api_struct->scale = magic_scale;
+      magic_api_struct->rotate_scale = magic_rotate_scale;
       magic_api_struct->touched = magic_touched;
 
 
@@ -22509,6 +22511,14 @@ static SDL_Surface *magic_scale(SDL_Surface * surf, int w, int h, int aspect)
   return (thumbnail2(surf, w, h, aspect, 1));
 }
 
+/**
+ * FIXME
+ */
+static SDL_Surface *magic_rotate_scale(SDL_Surface * surf, int r, int w)
+{
+  return (rotozoomSurface(surf, r, (float)w / surf->w, SMOOTHING_ON));
+}
+
 /**
  * FIXME
  */