hardlink: initial version

Hardlink consolidates duplicate files in a directory hierarchy with hardlinks,
similar to "nix-store --optimise".

IHMO, this program should be run by the default builder after $out has been set
up, to remove redundancy in the generated closures.

svn path=/nixpkgs/trunk/; revision=31934

pkgs/top-level/all-packages.nix

@@ -830,6 +830,8 @@ let
 
   pigz = callPackage ../tools/compression/pigz { };
 
+  hardlink = callPackage ../tools/system/hardlink { };
+
   halibut = callPackage ../tools/typesetting/halibut { };
 
   hddtemp = callPackage ../tools/misc/hddtemp { };