Empty version number, when downloading pandas as zip archive

[sfinkens]

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 ;)).

@Funkensieper sorry for the long delay. You're completely right, that's bad behaviour.
Will merge PR starting the next release cycle in a few days, which will give you
a version string of the form "0.13.0.dev" if git (or .git) aren't available.