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-numpy/package.py

@@ -0,0 +1,28 @@
+from spack import *
+
+class PyNumpy(Package):
+    """array processing for numbers, strings, records, and objects."""
+    homepage = "https://pypi.python.org/pypi/numpy"
+    url      = "https://pypi.python.org/packages/source/n/numpy/numpy-1.9.1.tar.gz"
+
+    version('1.9.1', '78842b73560ec378142665e712ae4ad9')
+    version('1.9.2', 'a1ed53432dbcd256398898d35bc8e645')
+    
+    extends('python')
+    depends_on('py-nose')
+    depends_on('netlib-blas+fpic')
+    depends_on('netlib-lapack+shared')
+
+    def patch(self):
+        filter_file(
+            "possible_executables = \['(gfortran|g77|ifort|efl)",
+            "possible_executables = ['fc",
+            "numpy/distutils/fcompiler/gnu.py",
+            "numpy/distutils/fcompiler/intel.py")
+
+    def install(self, spec, prefix):
+        with open('site.cfg', 'w') as f:
+            f.write('[DEFAULT]\n')
+            f.write('libraries=lapack,blas\n')
+            f.write('library_dirs=%s/lib:%s/lib\n' % (spec['blas'].prefix, spec['lapack'].prefix))
+        python('setup.py', 'install', '--prefix=%s' % prefix)