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-lockfile/package.py

@@ -0,0 +1,23 @@
+from spack import *
+
+class PyLockfile(Package):
+    """The lockfile package exports a LockFile class which provides a
+       simple API for locking files. Unlike the Windows msvcrt.locking
+       function, the fcntl.lockf and flock functions, and the
+       deprecated posixfile module, the API is identical across both
+       Unix (including Linux and Mac) and Windows platforms. The lock
+       mechanism relies on the atomic nature of the link (on Unix) and
+       mkdir (on Windows) system calls. An implementation based on
+       SQLite is also provided, more as a demonstration of the
+       possibilities it provides than as production-quality code.
+    """
+    homepage = "https://pypi.python.org/pypi/lockfile"
+    url      = "https://pypi.python.org/packages/source/l/lockfile/lockfile-0.10.2.tar.gz"
+
+    version('0.10.2', '1aa6175a6d57f082cd12e7ac6102ab15')
+
+    extends("python")
+    depends_on("py-setuptools")
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)