Add PythonPackage base class

- Add a PythonPackage class with build system support.
  - Support build phases in PythonPackage
  - Add a custom sanity check for PythonPackages
  - Get rid of nolink dependencies in python packages

- Update spack create to use new PythonPackage class

- Port most of Python packages to new PythonPackage class

- Conducted a massive install and activate of Python packages.
  - Fixed bugs introduced by install and activate.

- Update API docs on PythonPackage

var/spack/repos/builtin/packages/py-storm/package.py

@@ -22,19 +22,14 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-from spack import depends_on, extends, version
-from spack import Package
+from spack import *
 
 
-class PyStorm(Package):
+class PyStorm(PythonPackage):
     """Storm is an object-relational mapper (ORM) for Python"""
     homepage = "https://storm.canonical.com/"
     url      = "https://launchpad.net/storm/trunk/0.20/+download/storm-0.20.tar.gz"
 
     version('0.20', '8628503141f0f06c0749d607ac09b9c7')
 
-    extends('python')
     depends_on('py-setuptools', type='build')
-
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix=%s' % prefix)