Move all of NixOS to nixos/ in preparation of the repository merge

nixos/modules/installer/tools/nixos-checkout.nix

@@ -0,0 +1,55 @@
+# This module generates the nixos-checkout script, which replaces the
+# NixOS and Nixpkgs source trees in /etc/nixos/{nixos,nixpkgs} with
+# Git checkouts.
+
+{config, pkgs, ...}:
+
+with pkgs.lib;
+
+let
+
+  nixosCheckout = pkgs.substituteAll {
+    name = "nixos-checkout";
+    dir = "bin";
+    isExecutable = true;
+    src = pkgs.writeScript "nixos-checkout"
+      ''
+        #! ${pkgs.stdenv.shell} -e
+
+        if [ "$1" == "-h" ] || [ "$1" == "--help" ]; then
+          echo "Usage: `basename $0` [PREFIX]. See NixOS Manual for more info."
+          exit 0
+        fi        
+
+        prefix="$1"
+        if [ -z "$prefix" ]; then prefix=/etc/nixos; fi
+        mkdir -p "$prefix"
+        cd "$prefix"
+
+        if [ -z "$(type -P git)" ]; then
+            echo "installing Git..."
+            nix-env -iA nixos.pkgs.git || nix-env -i git
+        fi
+
+        # Move any old nixos or nixpkgs directories out of the way.
+        backupTimestamp=$(date "+%Y%m%d%H%M%S")
+
+        if [ -e nixos -a ! -e nixos/.git ]; then
+            mv nixos nixos-$backupTimestamp
+        fi
+
+        if [ -e nixpkgs -a ! -e nixpkgs/.git ]; then
+            mv nixpkgs nixpkgs-$backupTimestamp
+        fi
+
+        # Check out the NixOS and Nixpkgs sources.
+        git clone git://github.com/NixOS/nixos.git nixos
+        git clone git://github.com/NixOS/nixpkgs.git nixpkgs
+      '';
+   };
+
+in
+
+{
+  environment.systemPackages = [ nixosCheckout ];
+}