MPI support for HDF5 and SGE support for OpenMPI

### MPI

I added support for the Sun Grid Engine to openmpi. And, a new package `mpi4py`, which is a python interface to mpi.

### HDF5

I added mpi support to hdf5 (by default through openmpi). And, a new package `h5py`, which is a pythonic interface to hdf5 that also supports parallel hdf5.

In the [h5py derivation](https://github.com/aherrmann/nixpkgs/blob/1e0605738a94d834c97d6e7b9d1fc920f649facb/pkgs/development/python-modules/h5py/default.nix#L5-L10) I'm checking if both `hdf5`, and `h5py` have mpi support activated, and if so, if the mpi version is the same. Please let me know if this is the proper way to do these types of checks.

Let me know, if there is something that you would prefer to be done in a different way. I'll be happy to adjust it and learn the proper Nix way.
@offlinehacker Thanks for your comment. The installation fails due to an issue between setuptools and distutils, otherwise. The corresponding mailing list conversation is [here](http://lists.science.uu.nl/pipermail/nix-dev/2014-July/013591.html). The setuptools issue tracker is [here](https://bitbucket.org/pypa/setuptools/issue/73/typeerror-dist-must-be-a-distribution). It can be fixed by overriding the configurePhase, and installPhase.

The reason for not putting it into `python-packages.nix` is the following. Looking at [another package](https://github.com/NixOS/nixpkgs/blob/02c99b7cd1d296fb492d42f7a24d1b54757d87e4/pkgs/top-level/haskell-packages.nix#L1025) that uses MPI I found that it has a parameter `mpi` that defaults to `openmpi`, but can, in principle, also be set to `mpich`. Please correct me if I'm wrong, but to my knowledge, the cleanest way to do this is to put the package into a separate `.nix` file and then `callPackage` it inside `python-packages.nix`.