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-matplotlib/package.py

@@ -0,0 +1,47 @@
+from spack import *
+import os
+
+class PyMatplotlib(Package):
+    """Python plotting package."""
+    homepage = "https://pypi.python.org/pypi/matplotlib"
+    url      = "https://pypi.python.org/packages/source/m/matplotlib/matplotlib-1.4.2.tar.gz"
+
+    version('1.4.2', '7d22efb6cce475025733c50487bd8898')
+    version('1.4.3', '86af2e3e3c61849ac7576a6f5ca44267')
+
+    extends('python', ignore=r'bin/nosetests.*$')
+
+    depends_on('py-pyside')
+    depends_on('py-ipython')
+    depends_on('py-pyparsing')
+    depends_on('py-six')
+    depends_on('py-dateutil')
+    depends_on('py-pytz')
+    depends_on('py-nose')
+    depends_on('py-numpy')
+
+    depends_on('qt')
+    depends_on('bzip2')
+    depends_on('tcl')
+    depends_on('tk')
+    depends_on('qhull')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)
+
+        if str(self.version) in ['1.4.2', '1.4.3']:
+            # hack to fix configuration file
+            config_file = None
+            for p,d,f in os.walk(prefix.lib):
+                for file in f:
+                    if file.find('matplotlibrc') != -1:
+                        config_file = join_path(p, 'matplotlibrc')
+                        print config_file
+            if config_file == None:
+                raise InstallError('could not find config file')
+            filter_file(r'backend      : pyside',
+                        'backend      : Qt4Agg',
+                        config_file)
+            filter_file(r'#backend.qt4 : PyQt4',
+                        'backend.qt4 : PySide',
+                        config_file)