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-ipython/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyIpython(Package):
+class PyIpython(PythonPackage):
     """IPython provides a rich toolkit to help you make the most out of using
        Python interactively."""
     homepage = "https://pypi.python.org/pypi/ipython"
@@ -35,13 +35,15 @@ class PyIpython(Package):
     version('3.1.0', 'a749d90c16068687b0ec45a27e72ef8f')
     version('2.3.1', '2b7085525dac11190bfb45bb8ec8dcbf')
 
-    extends('python')
     depends_on('py-pygments', type=('build', 'run'))
     depends_on('py-setuptools', type=('build', 'run'))
-    depends_on('py-backports-shutil-get-terminal-size', when="^python@:3.2.999")
-    depends_on('py-pathlib2', when="^python@:3.3.999")
-    depends_on('py-pickleshare')
-    depends_on('py-simplegeneric')
 
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix=%s' % prefix)
+    # These dependencies breaks concretization
+    # See https://github.com/LLNL/spack/issues/2793
+    # depends_on('py-backports-shutil-get-terminal-size', when="^python@:3.2.999")  # noqa
+    # depends_on('py-pathlib2', when="^python@:3.3.999")
+    depends_on('py-backports-shutil-get-terminal-size', type=('build', 'run'))
+    depends_on('py-pathlib2', type=('build', 'run'))
+
+    depends_on('py-pickleshare', type=('build', 'run'))
+    depends_on('py-simplegeneric', type=('build', 'run'))