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/ravel/package.py

@@ -0,0 +1,23 @@
+from spack import *
+
+class Ravel(Package):
+    """Ravel is a parallel communication trace visualization tool that
+       orders events according to logical time."""
+
+    homepage = "https://github.com/scalability-llnl/ravel"
+    url = 'https://github.com/scalability-llnl/ravel/archive/v1.0.0.tar.gz'
+
+    version('1.0.0', 'b25fece58331c2adfcce76c5036485c2')
+
+    # TODO: make this a build dependency
+    depends_on('cmake@2.8.9:')
+
+    depends_on('muster@1.0.1:')
+    depends_on('otf')
+    depends_on('otf2')
+    depends_on('qt@5:')
+
+    def install(self, spec, prefix):
+        cmake('-Wno-dev', *std_cmake_args)
+        make()
+        make("install")