Use the version property from the device.
Move abstract methods to end of file.
Use $device->version
More places to use $device->version
No need for this protected property anylonger.
Allow $exporter to be null.

It's not needed in all sync operations, and this allows us
to keep the type hint.
Don't include messages we know were deleted in this set.
Add simple factory for obtaining message objects.
Use Horde_ActiveSync::messageFactory()