get the path right when deleting the temporary virtualenv :-/
install git as standard
install Node.js, CoffeeScript, LESS
wrap more install steps in conditional blocks to save time when repeatedly re-provisioning
upgrade versions of Django and other packages in common_requirements.txt
bump box version to 2.1
test for the file /usr/local/bin/virtualenv rather than the virtualenv command, to sidestep the issue of whether /usr/local/bin is on root's path