Add check for minimum Python version
Merge pull request #1 from jonboulle/minpython

Add check for minimum Python version
upgrade virtualenv to 1.8.2 in setup.sh
Squashed commit of the following:

commit db2b9a9af75bf767ff6faa62aec8efaf5680f9c6
Author: Brian Wickman <wickman@twitter.com>
Date:   Thu Nov 15 11:01:41 2012 -0800

    less confusing error message