Callback interface that is notified before the client bus begins its initialization tasks. Also called after the server becomes unreachable, after {@link SessionExpirationListener SessionExpirationListeners} are notifiedthat the previous session has expired, but before each time the bus begins an attempt to reconnect to the server and establish a new session.
This callback is primarily of use to framework-style extensions to Errai, and is not expected to be of great value when creating applications directly on top of Errai.
@see SessionExpirationListener
@author Mike Brock