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-h5py/package.py

@@ -0,0 +1,19 @@
+from spack import *
+import re
+
+class PyH5py(Package):
+    """The h5py package provides both a high- and low-level interface to the HDF5 library from Python."""
+    homepage = "https://pypi.python.org/pypi/h5py"
+    url      = "https://pypi.python.org/packages/source/h/h5py/h5py-2.4.0.tar.gz"
+
+    version('2.4.0', '80c9a94ae31f84885cc2ebe1323d6758')
+    version('2.5.0', '6e4301b5ad5da0d51b0a1e5ac19e3b74')
+
+    extends('python', ignore=lambda f: re.match(r'bin/cy*', f))
+    depends_on('hdf5')
+    depends_on('py-numpy')
+    depends_on('py-cython')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'configure', '--hdf5=%s' % spec['hdf5'].prefix)
+        python('setup.py', 'install', '--prefix=%s' % prefix)