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/dtcmp/package.py

@@ -0,0 +1,20 @@
+import os
+from spack import *
+
+class Dtcmp(Package):
+    """The Datatype Comparison Library provides comparison operations and
+       parallel sort algorithms for MPI applications."""
+
+    homepage = "https://github.com/hpc/dtcmp"
+    url      = "https://github.com/hpc/dtcmp/releases/download/v1.0.3/dtcmp-1.0.3.tar.gz"
+
+    version('1.0.3', 'cdd8ccf71e8ff67de2558594a7fcd317')
+
+    depends_on('mpi')
+    depends_on('lwgrp')
+
+    def install(self, spec, prefix):
+        configure("--prefix=" + prefix,
+                  "--with-lwgrp=" + spec['lwgrp'].prefix)
+        make()
+        make("install")