Installing dev version with pip is not supported
I've tried to install the dev version with `pip`, but it did not work. I had to manually download the tarball and run `python setup.py install`, which breaks a 100% pip setup of my local environment.

The following did not work:

```
pip install -e git+git://github.com/pydata/pandas.git#egg=pandas
```

It also did not work with the v0.8.0b1 version:

```
pip install -e git+git://github.com/pydata/pandas.git@v0.8.0b1#egg=pandas
```
