[devel] Bump to version libpng-1.5.0beta04

pngtest.c

@@ -1625,4 +1625,4 @@ main(int argc, char *argv[])
 }
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef version_1_5_0beta03 your_png_h_is_not_version_1_5_0beta03;
+typedef version_1_5_0beta04 your_png_h_is_not_version_1_5_0beta04;