GtkTreeView heads up

[Jonathan Blandford <jrb redhat com>]

I just made a lot of internal changes to the GtkTreeView widget, adding
incremental reflow support.  This should be the last structural change
that the tree goes through.  I'm not 100% sure I got all the bugs out,
and I'm pretty sure I introduced some new ones.  Please file bugs when
you find them.  On the plus side, the tree will now seem much faster,
and the annoying column bugs should be mostly gone.

Thanks,
-Jonathan