Merge branch 'features/python-modules' into features/memaxes

lib/spack/spack/build_environment.py

lib/spack/spack/cmd/clean.py

lib/spack/spack/cmd/extensions.py

lib/spack/spack/directory_layout.py

lib/spack/spack/hooks/extensions.py

lib/spack/spack/package.py

var/spack/packages/geos/package.py

var/spack/packages/py-basemap/package.py

var/spack/packages/py-biopython/package.py

var/spack/packages/py-gnuplot/package.py

var/spack/packages/py-libxml2/package.py

var/spack/packages/py-matplotlib/package.py

var/spack/packages/py-pyside/package.py

var/spack/packages/py-shiboken/package.py

var/spack/packages/python/package.py

var/spack/packages/qt/package.py