Add test for sdist and pandas import
As a follow-on to #9827, add a test for packaging pandas and importing that package into a venv that does not contain cython via https://github.com/pydata/pandas/wiki/Release-Checklist:
- python setup.py sdist --formats=zip,gztar
- create virtualenv with pandas dependencies (requirements_dev.txt), minus cython
- pip install <path_to_dist_tar.gz>
- run some subset of nosetests once installed
