mpi4py: Disable for Python3 and PyPy

Builds for Python3 and PyPy are failing at the moment [1-3]. Therefore, they
are disabled.

[1]: https://github.com/NixOS/nixpkgs/pull/3938#issuecomment-54750065
[2]: http://hydra.nixos.org/build/13993137/nixlog/1/raw
[3]: http://hydra.nixos.org/build/13873028/log/raw

pkgs/development/python-modules/mpi4py/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, python, buildPythonPackage, mpi, openssh }:
+{ stdenv, fetchurl, python, buildPythonPackage, mpi, openssh, isPy3k, isPyPy }:
 
 buildPythonPackage rec {
   name = "mpi4py-1.3.1";
@@ -45,6 +45,8 @@ buildPythonPackage rec {
   # if openssh is not present. E.g. h5py with mpi support.
   propagatedBuildInputs = [ openssh ];
 
+  disabled = isPy3k || isPyPy;
+
   meta = {
     description =
       "Python bindings for the Message Passing Interface standard";