Fix on `Session.renew_access_token`

When just the client_token is used `Session.auth` is `None` when refreshing  a token. I'm providing a patch to deal with this and on call `Session.auth.get()` when is was defined (eg.: Application key/secret pair authentication)

Also, some PEP8 file formatting was applied, and deprecations (like `has_key()`) was removed.