[gtkmm] Gdk::Pixbuf data storage

[Jonathan Brandmeyer <jbrandmeyer earthlink net>]

I am using the Pixbuf class to load image data for use as an OpenGL
texture and I ran across something strange - the images appear to be
upside-down.  OpenGL uses a bottom-row-first storage order for pixel
data.  Is Gdk::Pixbuf's storage order top-row-first?  I just want to
make sure I haven't made a mistake in my code.

Thanks,
Jonathan Brandmeyer