incompatibility with setuptools / easy_install

When these are installed, the installed script is wrong:

```
$ cat `which discodop`
#!/usr/bin/python3
# EASY-INSTALL-SCRIPT: 'disco-dop==0.5rc1','discodop'
__requires__ = 'disco-dop==0.5rc1'
__import__('pkg_resources').run_script('disco-dop==0.5rc1', 'discodop')
```

The workaround is to remove these (e.g. `pip uninstall setuptools` and `apt-get remove python-setuptools`).