This new class provides a proxy class for oauth2-based web services, such as the
new facebook graph API.  The basic idea is as follows:
- Construct a OAuth2Proxy object
- Build a login url with _build_login_url(_full)()
- Display said url in a browser widget (e.g. webkit) and listen for redirects to
  the specified 'redirect_uri'
- Extract the access token from the uri that you are redirected to
- Set the access token for the proxy with _set_access_token()

http://bugs.meego.com/show_bug.cgi?id=2265