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-mysqldb1/package.py

@@ -25,15 +25,14 @@
 from spack import *
 
 
-class PyMysqldb1(Package):
+class PyMysqldb1(PythonPackage):
     """Legacy mysql bindings for python"""
     homepage = "https://github.com/farcepest/MySQLdb1"
     url      = "https://github.com/farcepest/MySQLdb1/archive/MySQLdb-1.2.5.tar.gz"
 
-    version('1.2.5', '332c8f4955b6bc0c79ea15170bf7321b')
+    version('1.2.5', '332c8f4955b6bc0c79ea15170bf7321b',
+            url="https://github.com/farcepest/MySQLdb1/archive/MySQLdb-1.2.5.tar.gz")
+
+    # FIXME: Missing dependency on mysql
 
-    extends('python')
     depends_on('py-setuptools', type='build')
-
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix=%s' % prefix)