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/scr/package.py

@@ -0,0 +1,44 @@
+##############################################################################
+# Copyright (c) 2013, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://scalability-llnl.github.io/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License (as published by
+# the Free Software Foundation) version 2.1 dated February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+class Scr(Package):
+    """SCR caches checkpoint data in storage on the compute nodes of a
+       Linux cluster to provide a fast, scalable checkpoint/restart
+       capability for MPI codes"""
+
+    homepage = "https://computation.llnl.gov/project/scr/"
+
+    depends_on("mpi")
+#    depends_on("dtcmp")
+
+    version('1.1-7', 'a5930e9ab27d1b7049447c2fd7734ebd', url='http://downloads.sourceforge.net/project/scalablecr/releases/scr-1.1-7.tar.gz')
+    version('1.1.8', '6a0f11ad18e27fcfc00a271ff587b06e', url='https://github.com/hpc/scr/releases/download/v1.1.8/scr-1.1.8.tar.gz')
+
+    def install(self, spec, prefix):
+        configure("--prefix=" + prefix,
+                  "--with-scr-config-file=" + prefix + "/etc/scr.conf")
+        make()
+        make("install")