Also cache DropboxSession on Flask.g not class instance. The token is registered on this instance, and it must not be shared between users.
Use a tuple to persist the Dropbox credentials. Will be compatable with the new default session storage in Flask 0.10 which is JSON based.
Cleanup unused import
Save OAuthToken as a JSON serializable for compat with Flask 0.10
Merge pull request #8 from plain-vanilla-games/master

Flask 0.10 compatability