Update captured Janrain attributes upon login

When users log in, their attributes from Janrain are persisted locally via the
set_capturable_params method. If one of these attributes is changed between
logins, the updated value is not persisted in the application's database upon
the next login. If the application using Devise::Capturable relies on any of
these values, it may be working with stale data as a result.

Fix by making sure set_capturable_params is called on a user that is already
persisted, before reporting a successful login within the Devise.
Merge pull request #9 from oreillymedia/always-set-capturable-params

Update captured Janrain attributes upon login