TreeView column widths

[Joaquim Schmidlap <schmidlap schmidlap org>]

I have a TreeView that starts out displaying N columns. The TreeView  
is contained in a ScrolledWindow, which is on a page in a Notebook,  
which lives on the top level Window. The ScrolledWindow is set to  
POLICY_NEVER on the X axis, and POLICY_AUTOMATIC on the Y.

The user can elect to "hide" certain columns on the TreeView. After  
they are hidden, though, the rightmost column of the TreeView expands  
in width to fill whatever space the now-hidden columns used, with the  
net effect that the TreeView is always the same width.

 What I'd like is for the containing widgets all the way up to just  
get smaller as the columns are hidden (and grow again when they  
resurface). What's the best approach for this?