Added httplib2 to the installation requirements.

Author: joestump

setup.py

@@ -9,6 +9,7 @@
       author_email="[email protected]",
       url="http://github.com/simplegeo/python-oauth2",
       packages = find_packages(),
+      install_requires = ['httplib2'],
       license = "MIT License",
       keywords="oauth",
       zip_safe = True,