Permit field repetition in each part of vertically split tables,

Permit field repetition in each part of vertically split tables,
provided the values all match:
(caseen): New.
(xundump): Initialize and finalize it.
(xundump2): Update it.
(deffld): Deal with repetition.
(fldval_must_match): New, considers repetition as well as NSC_CONST.
(setnum, setstr): Use it.