xorg: set GLXVBlank to true when using nouveau driver to fix flickering issues

postplug.d/30xorg

@@ -323,13 +323,19 @@ if [ "$CONFCREATED" = "1" ]; then
         DefaultColorDepth 24' $XORGCONF ;;
    esac
 
-   # Compiz/3d configuration options 
+   # NVIDIA Compiz/3d configuration options 
    if [ "$VIDEODRIVER" == "nvidia" ]; then
       sed -i -e '/Section "Screen"/a\
         Option	"AddARGBGLXVisuals" "true"\
         Option	"DisableGLXRootClipping" "true"' $XORGCONF
    fi
 
+   # Nouveau configuration options 
+   if [ "$VIDEODRIVER" == "nouveau" ]; then
+      sed -i -e '/Driver.*"nouveau"/a\
+        Option      "GLXVBlank" "true"' $XORGCONF
+   fi
+
    # configure VirtualBox mouse driver
    if [ "$VIDEODRIVER" = "vboxvideo" ]; then
       sed -i "s|\"mouse\"|\"vboxmouse\"|" $XORGCONF