need to check gtk version before calling gtk-image-menu-item-set-always-show-image

http://library.gnome.org/devel/gtk/stable/GtkImageMenuItem.html#gtk-image-menu-item-set-always-show-image

If TRUE, the menu item will ignore the "gtk-menu-images" setting and always show the image, if available.

Use this property if the menuitem would be useless or hard to use without the image.

image_menu_item :
 a GtkImageMenuItem

always_show :
 TRUE if the menuitem should always show the image

Since 2.16

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This breaks on platforms that use older version of gtk, e.g. hardy.