install_package "yaml-0.1.4" "http://pyyaml.org/download/libyaml/yaml-0.1.4.tar.gz#36c852831d02cf90508c29852361d01b" --if needs_yaml
install_package "rubinius-2.0.0" "http://releases.rubini.us/rubinius-2.0.0.tar.bz2#62e379e044c822b81e7b20a27daf133e" rbx