Fix threading bug between previous day and today.
Fix threading bug between previous day and today.

- Just after midnight, process_previous_days_thread can start processing
the same files that processtoday_thread is still working on.  Add
processtoday_daydir global to track what day processtoday_thread is working on
and have process_previous_days_thread ignore that day.

dougkerr/surveillance,NeighborhoodGuard/communityview,NeighborhoodGuard/communityview,dougkerr/surveillance,NeighborhoodGuard/communityview,dougkerr/surveillance,dougkerr/surveillance,NeighborhoodGuard/communityview,dougkerr/surveillance,NeighborhoodGuard/communityview