generate_instances_sync
Description:
public void generate_instances_sync (long start, long end, Cancellable? cancellable, RecurInstanceCb cb)
  
  Does a combination of get_object_list and recur_generate_instances_sync.
The callback function should do a @ref of the calendar component it gets passed if it intends to keep it around, since it will be unreffed as soon as the callback returns.
Parameters:
| this | A calendar client | 
| start | Start time for query | 
| end | End time for query | 
| cancellable | a Cancellable; can be null | 
| cb | Callback for each generated instance | 
| cb_data | Closure data for the callback |