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-pypar/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyPypar(Package):
+class PyPypar(PythonPackage):
     """Pypar is an efficient but easy-to-use module that allows programs
        written in Python to run in parallel on multiple processors and
        communicate using MPI."""
@@ -34,13 +34,11 @@ class PyPypar(Package):
 
     version('2.1.5_108', '7a1f28327d2a3b679f9455c843d850b8')
 
-    extends('python')
     depends_on('mpi')
-    depends_on('py-numpy')
-
-    def install(self, spec, prefix):
-        with working_dir('source'):
-            setup_py('install', '--prefix=%s' % prefix)
+    depends_on('py-numpy', type=('build', 'run'))
 
     def url_for_version(self, version):
         return "https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/pypar/pypar-%s.tgz" % version
+
+    def build_directory(self):
+        return 'source'