Make overlays the default output mode for OS X only.

src/conio/ciolib.c

@@ -285,7 +285,10 @@ CIOLIBEXPORT int CIOLIBCALL initciolib(int mode)
 	switch(mode) {
 		case CIOLIB_MODE_AUTO:
 #if defined(WITH_SDL) || defined(WITH_SDL_AUDIO)
-			if(!try_sdl_init(mode))
+#if (defined(__MACH__) && defined(__APPLE__))
+			if(!try_sdl_init(CIOLIB_MODE_SDL_YUV))
+#endif
+			if(!try_sdl_init(CIOLIB_MODE_SDL))
 #endif
 #ifdef _WIN32
 				if(!try_conio_init(mode))