Merge Kevin, Ben, and Saravan's contributions into develop

bin/spack

lib/spack/llnl/util/filesystem.py

lib/spack/spack/build_environment.py

lib/spack/spack/concretize.py

lib/spack/spack/error.py

lib/spack/spack/package.py

lib/spack/spack/spec.py

lib/spack/spack/test/concretize.py

lib/spack/spack/test/directory_layout.py

lib/spack/spack/test/spec_semantics.py

lib/spack/spack/util/executable.py

var/spack/packages/arpack/package.py

var/spack/packages/atlas/package.py

var/spack/packages/boxlib/package.py

var/spack/packages/cblas/package.py

var/spack/packages/cgm/package.py

var/spack/packages/hypre/package.py

var/spack/packages/lapack/package.py

var/spack/packages/metis/package.py

var/spack/packages/netlib-blas/package.py