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-h5py/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyH5py(Package):
+class PyH5py(PythonPackage):
     """The h5py package provides both a high- and low-level interface to the
     HDF5 library from Python."""
 
@@ -38,8 +38,6 @@ class PyH5py(Package):
 
     variant('mpi', default=True, description='Build with MPI support')
 
-    extends('python')
-
     # Build dependencies
     depends_on('py-cython@0.19:', type='build')
     depends_on('pkg-config', type='build')
@@ -55,11 +53,11 @@ class PyH5py(Package):
     # Runtime dependencies
     depends_on('py-six', type=('build', 'run'))
 
-    def install(self, spec, prefix):
-        setup_py('configure', '--hdf5={0}'.format(spec['hdf5'].prefix))
+    phases = ['configure', 'install']
+
+    def configure(self, spec, prefix):
+        self.setup_py('configure', '--hdf5={0}'.format(spec['hdf5'].prefix))
 
         if '+mpi' in spec:
             env['CC'] = spec['mpi'].mpicc
-            setup_py('configure', '--mpi')
-
-        setup_py('install', '--prefix={0}'.format(prefix))
+            self.setup_py('configure', '--mpi')