Merge branch 'master' into stdenv-updates.

There were conflicts in pkgs/development/interpreters/ruby/ruby-19.nix,
which I resolved to the best of my knowledge. I'd appreciate if some of
the ruby gurus could have a look at the outcome of my merge, though.

pkgs/tools/text/html-tidy/default.nix

@@ -2,7 +2,7 @@
 
 let date = "2009-07-04"; in
   stdenv.mkDerivation rec {
-    name = "html-tidy-${date}";
+    name = "html-tidy-20090704";
 
     # According to http://tidy.sourceforge.net/, there are no new
     # release tarballs, so one has to either get the code from CVS or

pkgs/tools/text/numdiff/default.nix

@@ -0,0 +1,23 @@
+{ stdenv, fetchurl }:
+
+let
+  version = "5.6.1";
+in
+stdenv.mkDerivation {
+  name = "numdiff-${version}";
+  src = fetchurl {
+    url = "http://ftp.igh.cnrs.fr/pub/nongnu/numdiff/numdiff-${version}.tar.gz";
+    sha256 = "062byxp9vajj4flg1rqh0r2nwg9yx608mbsj5y25wkrzmkgcq3fx";
+  };
+  meta = {
+    description = ''
+      A little program that can be used to compare putatively similar files
+      line by line and field by field, ignoring small numeric differences
+      or/and different numeric formats.
+    '';
+    homepage = "http://www.nongnu.org/numdiff/";
+    license = stdenv.lib.licenses.gpl3Plus;
+    maintainers = stdenv.lib.maintainers.bbenoist;
+    platforms = stdenv.lib.platforms.gnu;
+  };
+}