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-biopython/package.py

@@ -0,0 +1,15 @@
+from spack import *
+
+class PyBiopython(Package):
+    """It is a distributed collaborative effort to develop Python libraries and applications which address the needs of current and future work in bioinformatics."""
+    homepage = "http://biopython.org/wiki/Main_Page"
+    url      = "http://biopython.org/DIST/biopython-1.65.tar.gz"
+
+    version('1.65', '143e7861ade85c0a8b5e2bbdd1da1f67')
+
+    extends('python')
+    depends_on('py-mx')
+    depends_on('py-numpy')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)