ECalBackendSync Base class for synchronous backends. @Returns: @backend: @lock: @backend: @cal: @read_only: @Returns: @backend: @cal: @address: @Returns: @backend: @cal: @address: @Returns: @backend: @cal: @attribute: @Returns: @backend: @cal: @capabiliites: @Returns: @backend: @cal: @only_if_exists: @username: @password: @Returns: @backend: @cal: @Returns: @backend: @cal: @calobj: @uid: @Returns: @backend: @cal: @calobj: @mod: @old_object: @new_object: @Returns: @backend: @cal: @uid: @rid: @mod: @old_object: @object: @Returns: @backend: @cal: @uid: @rid: @attachments: @Returns: @backend: @cal: @uid: @auid: @Returns: @backend: @cal: @calobj: @Returns: @backend: @cal: @calobj: @users: @modified_calobj: @Returns: @backend: @cal: @object: @Returns: @backend: @cal: @uid: @rid: @object: @Returns: @backend: @cal: @sexp: @objects: @Returns: @backend: @cal: @tzid: @object: @Returns: @backend: @cal: @tzobj: @Returns: @backend: @cal: @tzid: @Returns: @backend: @cal: @tzobj: @Returns: @backend: @cal: @change_id: @adds: @modifies: @deletes: @Returns: @backend: @cal: @users: @start: @end: @freebusy: @Returns: