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-scientificpython/package.py

@@ -0,0 +1,16 @@
+from spack import *
+
+class PyScientificpython(Package):
+    """ScientificPython is a collection of Python modules for
+       scientific computing. It contains support for geometry,
+       mathematical functions, statistics, physical units, IO,
+       visualization, and parallelization."""
+
+    homepage = "https://sourcesup.renater.fr/projects/scientific-py/"
+    url      = "https://sourcesup.renater.fr/frs/download.php/file/4411/ScientificPython-2.8.1.tar.gz"
+    version('2.8.1', '73ee0df19c7b58cdf2954261f0763c77')
+
+    extends('python')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)