There is a race if a channel is invalidated during its preparation: the
'invalidated' signal is already emitted so the Shell will never notice.
We fix this by simply checking if the channel is already invalidated when
receiving it from telepathy-glib.
In the approving case, we reject the full ChannelDispatchOperation as we only
support approving one channel at the time.
https://bugzilla.gnome.org/show_bug.cgi?id=677457
As the Shell does more than observing channels (users can interact with them),
it has to be an Handler as well. We have to make sure that all the new
incoming text channels are handled by the Shell by default, so we make it an
Approver as well.
From an user point of view, the only difference is that Empathy's tray icon
will stop blicking when receiving new channels.
We rely on ChannelDispatcher.DelegateChannels() and PresentChannel() to
interact with Empathy. Those methods have been implemented in
telepathy-mission-control 5.9.0 and telepathy-glib 0.15.0.
