Forced commit for correct commit message.
Gtk 2.20.x got a bug fix because libpng 1.2 defines png_guint_32 as
unsigned long. However png 1.4.x fixed the problem, so png_guint_32 is now
properly defined as unsigned int. Now undo the fix in gtk so it uses a
unsigned int with png 1.4.
Submitted by: nox@