1) Change the MessageSender logic so that individual SMS messages
are encrypted whenever there is a secure session, unless the UI
explicitly specifies otherwise.
2) Change the MMS logic so that messages to a recipient with a
secure session are all sent individually, instead of including
those recipients into the batch plaintext message.
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!).
The 1.X Android versions don't have the 2.X VERSION_CODE
symbols, so comparing against them in order to make 1.6
choices will throw runtime exceptions.
