Const correctness patch for SDL_MapRGB and SDL_MapRGBA.

  Fixes Bugzilla #421.

include/SDL_video.h

@@ -447,13 +447,15 @@ extern DECLSPEC int SDLCALL SDL_SetPalette(SDL_Surface *surface, int flags,
  * Maps an RGB triple to an opaque pixel value for a given pixel format
  */
 extern DECLSPEC Uint32 SDLCALL SDL_MapRGB
-			(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b);
+(const SDL_PixelFormat * const format,
+ const Uint8 r, const Uint8 g, const Uint8 b);
 
 /*
  * Maps an RGBA quadruple to a pixel value for a given pixel format
  */
-extern DECLSPEC Uint32 SDLCALL SDL_MapRGBA(SDL_PixelFormat *format,
-				   Uint8 r, Uint8 g, Uint8 b, Uint8 a);
+extern DECLSPEC Uint32 SDLCALL SDL_MapRGBA
+(const SDL_PixelFormat * const format,
+ const Uint8 r, const Uint8 g, const Uint8 b, const Uint8 a);
 
 /*
  * Maps a pixel value into the RGB components for a given pixel format

src/video/SDL_pixels.c

@@ -337,7 +337,9 @@ Uint8 SDL_FindColor(SDL_Palette *pal, Uint8 r, Uint8 g, Uint8 b)
 }
 
 /* Find the opaque pixel value corresponding to an RGB triple */
-Uint32 SDL_MapRGB(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b)
+Uint32 SDL_MapRGB
+(const SDL_PixelFormat * const format,
+ const Uint8 r, const Uint8 g, const Uint8 b)
 {
 	if ( format->palette == NULL ) {
 		return (r >> format->Rloss) << format->Rshift
@@ -350,7 +352,9 @@ Uint32 SDL_MapRGB(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b)
 }
 
 /* Find the pixel value corresponding to an RGBA quadruple */
-Uint32 SDL_MapRGBA(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b, Uint8 a)
+Uint32 SDL_MapRGBA
+(const SDL_PixelFormat * const format,
+ const Uint8 r, const Uint8 g, const Uint8 b, const Uint8 a)
 {
 	if ( format->palette == NULL ) {
 	        return (r >> format->Rloss) << format->Rshift