task_add_completed
Description:
Adds a Task:completed property value into the builder, which should have started an object member.
When the value is 0, then adds a NULL-object, to indicate removal of the property.
Parameters:
| builder | a Builder with a started object member | 
| value | a Task::completed property value, as Unix time | 
Namespace: E.GData
  
  Package: libedataserver-1.2