Updating setup.py and MANIFEST to include all subdirs.

MANIFEST.in

@@ -1 +1,2 @@
 include README.md
+recursive-exclude tests *

setup.py

@@ -28,12 +28,9 @@
     print('oauth2client requires python3 version >= 3.3.', file=sys.stderr)
     sys.exit(1)
 
+from setuptools import find_packages
 from setuptools import setup
 
-packages = [
-    'oauth2client',
-]
-
 install_requires = [
     'httplib2>=0.9.1',
     'pyasn1>=0.1.7',
@@ -55,7 +52,7 @@
     author="Google Inc.",
     url="https://github.com/google/oauth2client/",
     install_requires=install_requires,
-    packages=packages,
+    packages=find_packages(),
     license="Apache 2.0",
     keywords="google oauth 2.0 http client",
     classifiers=[