Some fixes recommended by PyCharm

.gitignore

lib/spack/spack/architecture.py

lib/spack/spack/color.py

lib/spack/spack/compilation.py

lib/spack/spack/directory_layout.py

lib/spack/spack/multimethod.py

lib/spack/spack/packages/__init__.py

lib/spack/spack/test/spec_dag.py

lib/spack/spack/test/spec_semantics.py

lib/spack/spack/test/spec_syntax.py

lib/spack/spack/url.py

lib/spack/spack/util/none_high.py

lib/spack/spack/util/none_low.py

lib/spack/spack/version.py