magic expand flag on GtkWidget

[Havoc Pennington <hp pobox com>]

Hi,

This is a major enough change it should probably hit the list and not
just bugzilla:
https://bugzilla.gnome.org/show_bug.cgi?id=628902

The patch needs finishing as noted in the bug but you can already play
with it, it just is missing some production details.

Havoc