Enable/disable libreoffice build in nixpkgs.config, not in tree.

I've tried to use override instead of getConfig but failed because exception is
thrown before the function is called with force = true.

svn path=/nixpkgs/trunk/; revision=32131

pkgs/applications/office/openoffice/libreoffice.nix

@@ -6,10 +6,13 @@
 , libXinerama, openssl, gperf, cppunit, GConf, ORBit2
 , autoconf, openldap, postgresql, bash
 , langs ? [ "en-US" "ca" "ru" "eo" "fr" "nl" "de" "en-GB" ]
+, force ? false
 }:
 
-throw "The expression for libreoffice is still not ready"
-
+if !force then
+  throw ''The expression for libreoffice is still not ready.
+  Set config.libreoffice.force = true; if you want to try it anyway.''
+else
 stdenv.mkDerivation rec {
   name = "libreoffice-3.4.5.2";
 

pkgs/top-level/all-packages.nix

@@ -7157,6 +7157,7 @@ let
   libreoffice = callPackage ../applications/office/openoffice/libreoffice.nix {
     inherit (perlPackages) ArchiveZip CompressZlib;
     inherit (gnome) GConf ORBit2;
+    force = getConfig [ "libreoffice" "force" ] false;
   };
 
   lingot = callPackage ../applications/audio/lingot {