Don't install tests, but do ship them in the tarball

Also picks up some missing files in tests/assets and tests/assets2

MANIFEST.in

 recursive-include pipeline/templates *.html *.jinja
 include AUTHORS LICENSE README.rst HISTORY.rst
+recursive-include tests *
+recursive-exclude tests *.pyc *.pyo

setup.py

@@ -12,7 +12,7 @@ setup(
     author_email='timothee.peignier@tryphon.org',
     url='https://github.com/cyberdelia/django-pipeline',
     license='MIT',
-    packages=find_packages(),
+    packages=find_packages(exclude=['tests']),
     zip_safe=False,
     install_requires=[
         'futures>=2.1.3',