Monkeypatch matplotlib and pyplot's show functions to work

A cleaner solution would be to use something like IPython's InlineBackend.
Install pandas and scikit-learn into Sage in the VM
fix bugs in install-sagecell script
Don't su to sageserver --- sageserver can't chown, etc.
Be more explicit about printing errors
Fix extra package installation
Add patsy and statsmodels packages to installation

Thanks to Harald Schilly for pointing these out.
Add *very* experimental dynamic functionality