GtkTreeView: space between two column since 2.6

[Andreas Bachmann <bachi te-clan ch>]

Hi!

I'm developing a gtk+ based equivalent to 'netstat' and 'sockstat'.
the app is at the moment just for freebsd machines runnable, since i'm
using kernel structures (sysctl xsocket and xfile).
but my problem is not freebsd-specific.
between two GtkTreeViewColumns, a gray 1-2 pixel wide vertical bar is
visibel since 2.6... with 2.4, there is no vertical bar.
http://bachi.te-clan.ch/tcpview.png
the red rows are developed with GtkCellRender's property
"cell-background" = "Red".
http://bachi.te-clan.ch/TCPView-0.2.tar.gz

how to I stash the vertical bar away?

greets

Andreas Bachmann