More fixes/changes

- environment.sh updated to prepend $PYTHONPATH with $vpython automatically on soolin;
- cutflow script updated — luminosity is now scaled according to the main configuration, all the yields are straight from the histograms, before the fit;
- more fixes like errors() -> yerravg() for rootpy histograms;
- rootpy itself updated to fix the bug mentioned in #67;
- in control plots, MC uncertainty is now centrally set to 10%. This needs revision, as this is technically not the ttbar uncertainty, but the uncertainty applied to the whole MC stack;
- minor changes to 04_make_plots_matplotlib.py (now works again on soolin).