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-tuiview/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyTuiview(Package):
+class PyTuiview(PythonPackage):
     """TuiView is a lightweight raster GIS with powerful raster attribute
     table manipulation abilities.
     """
@@ -35,10 +35,6 @@ class PyTuiview(Package):
 
     version('1.1.7', '4b3b38a820cc239c8ab4a181ac5d4c30')
 
-    extends("python")
     depends_on("py-pyqt", type=('build', 'run'))
     depends_on("py-numpy", type=('build', 'run'))
     depends_on("gdal")
-
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix=%s' % prefix)