Transfer series don't transfer custom regressors and specification

When transferring series which depend on custon regressors (or custon specifications), the folders **X13Spec** and **Variables** are not copied.

1) the regressors are missing. But it can be resolved with rewrinting of transfer_series with a copy of the Variable folder.
2) the pre-specified specifications are missing and are written in the SAP files.

Even if the metadata of the series are updated, the metadata of the regressors are missing. So the workspace can't be updated.