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-wcsaxes/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyWcsaxes(Package):
+class PyWcsaxes(PythonPackage):
     """WCSAxes is a framework for making plots of Astronomical data
     in Matplotlib."""
 
@@ -34,10 +34,7 @@ class PyWcsaxes(Package):
 
     version('0.8', 'de1c60fdae4c330bf5ddb9f1ab5ab920')
 
-    extends('python', ignore=r'bin/pbr')
+    extends('python', ignore=r'bin/')
     depends_on('py-numpy', type=('build', 'run'))
     depends_on('py-matplotlib', type=('build', 'run'))
     depends_on('py-astropy', type=('build', 'run'))
-
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix={0}'.format(prefix))