Add workaround for GTK+ bug 632538
Add Juha Sahakangas
Add workaround for GTK+ bug 632538

Fix the AttributeError ("'gobject.GProps' object has no attribute
'gtk_button_images'") exception that is sometimes raised in versions
of GTK+ older than 2.24.19. Thanks to Scott Engle for reporting this
problem (#18) and Juha Sahakangas for helping us understand what was
going wrong and telling us the workaround.

https://bugzilla.gnome.org/show_bug.cgi?id=632538

This merges branch 'gtk-bug-632538-workaround'