Empty version number, when downloading pandas as zip archive
When you download the current master as zip archive from github.com, assigning a version number fails (empty string). As a consequence, packages depending on pandas (e.g. statsmodels) will fail to build as well.
I assume, the reason is the following: The version number is determined using git, but since the downloaded archive is not a git repository, this action fails and the version number remains an empty string.

I dont't think, this should be changed, but it would be helpful, if you added a node in the installation instruction, e.g. for people intending to install pandas on a machine without internet connection (like me ;)).
