New, cleaner package repository structure.

Package repositories now look like this:

    top-level-dir/
        repo.yaml
        packages/
            libelf/
                package.py
            mpich/
                package.py
            ...

This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).

var/spack/repos/builtin/packages/parmetis/package.py

@@ -0,0 +1,26 @@
+from spack import *
+
+class Parmetis(Package):
+    """ParMETIS is an MPI-based parallel library that implements a
+       variety of algorithms for partitioning unstructured graphs,
+       meshes, and for computing fill-reducing orderings of sparse
+       matrices."""
+    homepage = "http://glaros.dtc.umn.edu/gkhome/metis/parmetis/overview"
+    url      = "http://glaros.dtc.umn.edu/gkhome/fetch/sw/parmetis/parmetis-4.0.3.tar.gz"
+
+    version('4.0.3', 'f69c479586bf6bb7aff6a9bc0c739628')
+
+    depends_on('mpi')
+
+    def install(self, spec, prefix):
+        cmake(".",
+              '-DGKLIB_PATH=%s/metis/GKlib' % pwd(),
+              '-DMETIS_PATH=%s/metis' % pwd(),
+              '-DSHARED=1',
+              '-DCMAKE_C_COMPILER=mpicc',
+              '-DCMAKE_CXX_COMPILER=mpicxx',
+              '-DSHARED=1',
+              *std_cmake_args)
+
+        make()
+        make("install")