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/metis/package.py

@@ -0,0 +1,27 @@
+from spack import *
+
+class Metis(Package):
+    """METIS is a set of serial programs for partitioning graphs,
+       partitioning finite element meshes, and producing fill reducing
+       orderings for sparse matrices. The algorithms implemented in
+       METIS are based on the multilevel recursive-bisection,
+       multilevel k-way, and multi-constraint partitioning schemes."""
+
+    homepage = "http://glaros.dtc.umn.edu/gkhome/metis/metis/overview"
+    url      = "http://glaros.dtc.umn.edu/gkhome/fetch/sw/metis/metis-5.1.0.tar.gz"
+
+    version('5.1.0', '5465e67079419a69e0116de24fce58fe')
+
+    depends_on('mpi')
+
+    def install(self, spec, prefix):
+        cmake(".",
+              '-DGKLIB_PATH=%s/GKlib' % pwd(),
+              '-DSHARED=1',
+              '-DCMAKE_C_COMPILER=mpicc',
+              '-DCMAKE_CXX_COMPILER=mpicxx',
+              '-DSHARED=1',
+              *std_cmake_args)
+
+        make()
+        make("install")