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/py-python-daemon/package.py

@@ -0,0 +1,26 @@
+from spack import *
+
+class PyPythonDaemon(Package):
+    """Library to implement a well-behaved Unix daemon process.
+
+       This library implements the well-behaved daemon specification of
+       PEP Standard daemon process.
+
+       A well-behaved Unix daemon process is tricky to get right, but the
+       required steps are much the same for every daemon program. A
+       DaemonContext instance holds the behaviour and configured process
+       environment for the program; use the instance as a context manager
+       to enter a daemon state.
+    """
+    homepage = "https://pypi.python.org/pypi/python-daemon/"
+    url      = "https://pypi.python.org/packages/source/p/python-daemon/python-daemon-2.0.5.tar.gz"
+
+    version('2.0.5', '73e7f49f525c51fa4a995aea4d80de41')
+
+    extends("python")
+    depends_on("py-setuptools")
+    depends_on("py-lockfile")
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)
+