install_package "yaml-0.1.4" "http://pyyaml.org/download/libyaml/yaml-0.1.4.tar.gz#36c852831d02cf90508c29852361d01b" --if needs_yaml
install_package "rubinius-2.2.1" "http://releases.rubini.us/rubinius-2.2.1.tar.bz2#83c4d61d5fdb070d11babd867852277b" rbx