1) In addition to the Recipient interface, there is now
RecipientDevice. A Recipient can have multiple corresponding
RecipientDevices. All addressing is done to a Recipient, but
crypto sessions and transport delivery are done to
RecipientDevice.
2) The Push transport handles the discovery and session setup
of additional Recipient devices.
3) Some internal rejiggering of Groups.
1) Switch back from AsyncTasks to an Executor and Futures.
2) Make the Executor operate LIFO.
3) Make the Executor thread a BACKGROUND_PRIORITY thread.
1) Refactor recipient class to support asynchronous loading operations.
2) Refactor recipient factory to simplify recipient access.
3) Consoliate everything into one recipient provider that is capable of
doing async lookups and intelligent caching.
This requires a few changes to Recipient in order to make sure we
have a Contact URI at click time. While we're at it, let's git rid
of the OldRecipientProvider, which was for pre-2.0 contact stuff
(no longer supported, woohoo!).
