[libpng15] Bump version to 1.5.11beta01

pngtest.c

@@ -1817,4 +1817,4 @@ main(int argc, char *argv[])
 }
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_5_10 Your_png_h_is_not_version_1_5_10;
+typedef png_libpng_version_1_5_11beta01 Your_png_h_is_not_version_1_5_11beta01;