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/qhull/package.py

@@ -0,0 +1,27 @@
+from spack import *
+
+class Qhull(Package):
+    """Qhull computes the convex hull, Delaunay triangulation, Voronoi
+       diagram, halfspace intersection about a point, furt hest-site
+       Delaunay triangulation, and furthest-site Voronoi diagram. The
+       source code runs in 2-d, 3-d, 4-d, and higher dimensions. Qhull
+       implements the Quickhull algorithm for computing the convex
+       hull. It handles roundoff errors from floating point
+       arithmetic. It computes volumes, surface areas, and
+       approximations to the convex hull.
+
+       Qhull does not support triangulation of non-convex surfaces,
+       mesh generation of non-convex objects, medium-sized inputs in
+       9-D and higher, alpha shapes, weighted Voronoi diagrams,
+       Voronoi volumes, or constrained Delaunay triangulations."""
+
+    homepage = "http://www.qhull.org"
+
+    version('1.0', 'd0f978c0d8dfb2e919caefa56ea2953c',
+            url="http://www.qhull.org/download/qhull-2012.1-src.tgz")
+
+    def install(self, spec, prefix):
+        with working_dir('spack-build', create=True):
+            cmake('..', *std_cmake_args)
+            make()
+            make("install")