install_package "yaml-0.1.6" "http://pyyaml.org/download/libyaml/yaml-0.1.6.tar.gz#5fe00cda18ca5daeb43762b80c38e06e" --if needs_yaml
install_package "rubinius-2.1.1" "http://releases.rubini.us/rubinius-2.1.1.tar.bz2#6b4df0caec5ea88373e113f97a3b4c72" rbx