python-dateutils < 2 requirement for python 2. Is it necessary?
The most recent version (2.1) supports both 2.x and 3.x.

Pandas works for me using version 2.1:

```
(VENV)[~/ng]
$ nosetests pandas
...
...
----------------------------------------------------------------------
Ran 2228 tests in 112.553s

OK (SKIP=45)
(VENV)[~/ng]
$ python -c "import dateutil; print dateutil.__version__"
2.1
```

I suggest change setup.py.
