in sub-pixel unable to change "Unknown" to "Horizontal RGB"

[wojtek@xxxxxxxxxxxxxxxx (Wojtek Bogusz)]

Hello,

I am running XFree86 Version 4.3.0 with fontconfig 2.2.1 with the GNOME
2.4.0 on Mandrake 9.2 on the Thoshiba Satellite 1135-S155 laptop. And I
am trying to setup the sub-pixel antialiasing. I tried several ways
including the standard placing:

         <match target="font">
                 <edit name="rgba" mode="assign">
                         <const>rgb</const>
                 </edit>
         </match>

in the /etc/fonts/local.conf

But all the time I get "Unknown" sub-pixel order in

$ xdpyinfo -ext RENDER | grep sub-pix
     Screen 0 (sub-pixel order Unknown)

I have also try to find and change the key in the gconf-editor, in
/desktop/gnome/font_rendering/... But all without the success...

My question is: How to change the sub-pixel order from "Unknown" to 
"Horizontal RGB"?

Cheers,
Wojtek