Merge pull request #488 from LLNL/revert-477-refactoring/stage

lib/spack/llnl/util/filesystem.py

lib/spack/spack/cmd/clean.py

lib/spack/spack/mirror.py

lib/spack/spack/package.py

lib/spack/spack/stage.py

lib/spack/spack/test/concretize.py

lib/spack/spack/test/config.py

lib/spack/spack/test/configure_guess.py

lib/spack/spack/test/database.py

lib/spack/spack/test/directory_layout.py

lib/spack/spack/test/git_fetch.py

lib/spack/spack/test/hg_fetch.py

lib/spack/spack/test/install.py

lib/spack/spack/test/link_tree.py

lib/spack/spack/test/lock.py

lib/spack/spack/test/make_executable.py

lib/spack/spack/test/mirror.py

lib/spack/spack/test/mock_packages_test.py

lib/spack/spack/test/mock_repo.py

lib/spack/spack/test/multimethod.py