[PATCH] x/ythickness being override by combobox

["Alberto Ruiz" <aruiz gnome org>]

combobox overrides x/ythickness for the editable entry on list mode, I've opened a bug (#521442) and proposed a patch attached.

Is it okay to commit?

You can see the consecuences on a releated bug in #461805 attached images:
http://bugzilla.gnome.org/attachment.cgi?id=99629 (notice the lack of shadow on the editable entry)
http://bugzilla.gnome.org/attachment.cgi?id=92702 (same on the renderer)

For some reason the bug is not exposed on most commons egines though.
-- 
Un saludo,
Alberto Ruiz