Fix fields checks for split tables:

Fix fields checks for split tables:
(caseen): Remove.
(xufldhdr, deffld): Record only fields in this part in caflds[].  This
fixes the check for duplicate fields in parts other than the first.
(cafldspp): New, to record fields in previous parts.
(xundump): Initialize and finalize it.
(xufooter): Update it.  Requires new parameter ca.  Caller changed.
(fldval_must_match): Use it to do the right thing for split arrays.
(chkflds): Adapt for changed caflds[].
(chkflds): The check for missing fields was skipped for all parts of a
split table instead of for all but the final part.