Add Cython, because it's needed to build xpra.

pkgs/development/interpreters/cython/default.nix

@@ -0,0 +1,20 @@
+{ stdenv, fetchurl, python, pkgconfig }:
+
+stdenv.mkDerivation {
+  name = "cython-0.16";
+
+  src = fetchurl {
+    url = http://www.cython.org/release/Cython-0.16.tar.gz;
+    sha256 = "1yz6jwv25xx5mbr2nm4l7mi65gvpm63dzi3vrw73p51wbpy525lp";
+  };
+
+  buildPhase = "python setup.py build --build-base $out";
+
+  installPhase = "python setup.py install --prefix=$out";
+
+  buildInputs = [ python pkgconfig ];
+
+  meta = {
+    description = "An interpreter to help writing C extensions for Python";
+  };
+}

pkgs/top-level/all-packages.nix

@@ -1777,6 +1777,8 @@ let
 
   cmucl_binary = callPackage ../development/compilers/cmucl/binary.nix { };
 
+  cython = callPackage ../development/interpreters/cython { };
+
   dylan = callPackage ../development/compilers/gwydion-dylan {
     dylan = callPackage ../development/compilers/gwydion-dylan/binary.nix {  };
   };