Update SDL2 to 2.0.4

code/SDL2/include/SDL_timer.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -88,7 +88,7 @@ typedef int SDL_TimerID;
 /**
  * \brief Add a new timer to the pool of timers already running.
  *
- * \return A timer ID, or NULL when an error occurs.
+ * \return A timer ID, or 0 when an error occurs.
  */
 extern DECLSPEC SDL_TimerID SDLCALL SDL_AddTimer(Uint32 interval,
                                                  SDL_TimerCallback callback,