Remove padding in a GtkButton

[Jérôme Couderc <j couderc ifrance com>]

Hi,

    I've a little image (5x5 pixels) to display in a small button
(13x13 pixels) but it seems that there is padding (~3 pixels) in the
button that prevent to display the image correctly.
So there is only 3 pixels in the button to display an image of 5 pixels...

So, how can I remove this padding? (note that there is no problem on the
gtk-1.2 version)

Thanks in advance,
Jerome