#838 Follow mode states are not cleared when users leave the session

[Franz Zieris]

• A non-host follows some other session participant (this is represented in everyone's session view, including the one of the host).
• That user leaves the session (he is removed from the list of session participants, and -- since bug [#825] is fixed -- added to the list of the the other roster members again).
• The host re-invites that user: Now the host's session view says that user is again in follow mode -- which is not true.

It looks like the class maintaining the states of who is following whom does not listen the events of users leaving (and/or joining) the session so the old follow mode information is not updated.
(This problem probably also exists for other awareness information related classes -- in addition the in-session user events and the session life cycle they should also care about the user life cycle.)

[Stefan Rossbach]

a358619757442411e026a88e5f954c49d69ac3b4