Build .PYC files when Cython present, else use .C

With this change you are able to install the python module without any Makefiles: `python setup.py install` from within the directory and it's good to go. If the C files aren't already there (which they should be in a distribution downloaded from PyPI) then you'll get a warning about hadoofus.c not being present if you don't have Cython installed.

After installing the python module, libhadoofus separately needs to be findable or else you'll receive an ImportError when trying:

```bash
python -c "import hadoofus" && echo OK
# ImportError: /vagrant/env/local/lib/python2.7/site-packages/hadoofus.so: undefined symbol: HDFS_DATANODE_ERR_NO_CRCS

LD_PRELOAD=/vagrant/src/libhadoofus.so python -c "import hadoofus" && echo OK
# OK
```