zbar: ghostscript was missing for zbar

pkgs/tools/graphics/zbar/default.nix

@@ -1,6 +1,6 @@
 x@{builderDefsPackage
   , imagemagickBig, pkgconfig, python, pygtk, perl, libX11, libv4l
-  , qt4, lzma, gtk2
+  , qt4, lzma, gtk2, ghostscript
   , ...}:
 builderDefsPackage
 (a :  

pkgs/top-level/all-packages.nix

@@ -3620,6 +3620,7 @@ let
     pygtk = lib.overrideDerivation pygtk (x: {
       gtk = gtk2;
     });
+    ghostscript = ghostscriptX;
   };
 
   zdelta = callPackage ../tools/compression/zdelta { };