Added possibility to modify Xorg passed to upstart-job and xlaunch

svn path=/nixos/trunk/; revision=11555

system/options.nix

@@ -1315,6 +1315,14 @@
         ";
       };
 
+      packageFun = mkOption {
+        default = pkgs: pkgs.xorg;
+	description = "
+	  Alternative X.org package to use. For 
+	  example, you can replace individual drivers.
+	";
+      };
+
     };
 
     ejabberd = {

upstart-jobs/xserver.nix

@@ -10,7 +10,7 @@ let
 
   # Abbreviations.
   cfg = config.services.xserver;
-  xorg = pkgs.xorg;
+  xorg = cfg.packageFun pkgs;
   gnome = pkgs.gnome;
   stdenv = pkgs.stdenv;
 
@@ -160,6 +160,12 @@ let
         ';
       fi;
 
+      if [ "${toString videoDriver}" = ati ]; then
+        export extensions='
+          Option "Composite" "Enable"
+        ';
+      fi;
+
       substituteAll $src $out
     ''; # */
   };