$OpenBSD: patch-src_png_reader_cpp,v 1.1 2011/07/08 20:38:01 naddy Exp $

Fix build with png-1.5.

--- src/png_reader.cpp.orig	Tue Jul  5 18:18:28 2011
+++ src/png_reader.cpp	Tue Jul  5 18:18:53 2011
@@ -82,7 +82,7 @@ namespace mapnik
     {
         png_size_t check;
         check = (png_size_t)fread(data, (png_size_t)1, length,
-                                  (FILE *)png_ptr->io_ptr);
+                                  (FILE *)png_get_io_ptr(png_ptr));
 
         if (check != length)
         {
