Added the Undo key for the Atari keyboard

include/SDL_keysym.h

@@ -284,6 +284,7 @@ typedef enum {
 	SDLK_MENU		= 319,
 	SDLK_POWER		= 320,		/* Power Macintosh power key */
 	SDLK_EURO		= 321,		/* Some european keyboards */
+	SDLK_UNDO		= 322,		/* Atari keyboard has Undo */
 
 	/* Add any other keys here */
 

src/events/SDL_keyboard.c

@@ -316,6 +316,7 @@ int SDL_KeyboardInit(void)
 	keynames[SDLK_MENU] = "menu";
 	keynames[SDLK_POWER] = "power";
 	keynames[SDLK_EURO] = "euro";
+	keynames[SDLK_UNDO] = "undo";
 
 	/* Done.  Whew. */
 	return(0);