This also covers contacts in the 'added' set and the 'previously exported' set - these contacts' PAs are required for the adaptor, but they have no constituent for that adaptor.

I haven't really thought about what the sync adaptor should do to export these contacts and keep them in sync.  Probably just compare against a QContact stored at the last export - maybe we should provide a function that compares a contact (before, after) pair and produces a list of changes, for adaptors to use.