module compiled against API version 8 but this version of numpy is 7
After upgrading to pandas 0.11.0 using pip, I get the following errors:

```
In [1]: import pandas
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
RuntimeError: module compiled against API version 8 but this version of numpy is 7
numpy.core.multiarray failed to import
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-1-d6ac987968b6> in <module>()
----> 1 import pandas

/usr/local/lib/python2.7/site-packages/pandas/__init__.py in <module>()
      4 
      5 try:
----> 6     from . import hashtable, tslib, lib
      7 except Exception:  # pragma: no cover
      8     import sys

ImportError: numpy.core.multiarray failed to import
```

I have numpy version 1.7.1, running OS X 10.8.3
Installing pandas on an empty virtualenv failed due to a numpy dependency which couldn't install automatically, however, after installing numpy explicitly, it did work. Is this a bug or is something just messed up with my install?
