Install failure using pip?

Reported by a user via e-mail:

```
Python 2.7.7 |Anaconda 2.0.1 (64-bit)| (default, Jun  2 2014, 12:34:02) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-54)] on linux2
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>>> import astroquery
>>> from astroquery.simbad import Simbad
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/______/anaconda/lib/python2.7/site-packages/astroquery/simbad/__init__.py", line 14, in <module>
    class Conf(_config.ConfigNamespace):
AttributeError: 'module' object has no attribute 'ConfigNamespace'
```

I don't know what the problem is yet, but I suspect an astropy 0.3 + astroquery 0.2 incompatibility, which implies that we need a version requirement in `setup.cfg`