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/muster/package.py

@@ -0,0 +1,22 @@
+from spack import *
+
+class Muster(Package):
+    """The Muster library provides implementations of sequential and
+       parallel K-Medoids clustering algorithms. It is intended as a
+       general framework for parallel cluster analysis, particularly
+       for performance data analysis on systems with very large
+       numbers of processes.
+    """
+    homepage = "https://github.com/scalability-llnl/muster"
+    url      = "https://github.com/scalability-llnl/muster/archive/v1.0.tar.gz"
+
+    version('1.0.1', 'd709787db7e080447afb6571ac17723c')
+    version('1.0',   '2eec6979a4a36d3a65a792d12969be16')
+
+    depends_on("boost")
+    depends_on("mpi")
+
+    def install(self, spec, prefix):
+        cmake(".", *std_cmake_args)
+        make()
+        make("install")