[libpng16] Bump version to 1.6.9beta03

pngtest.c

@@ -1991,4 +1991,4 @@ main(void)
 #endif
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_6_9beta02 Your_png_h_is_not_version_1_6_9beta02;
+typedef png_libpng_version_1_6_9beta03 Your_png_h_is_not_version_1_6_9beta03;