Rewrite rev. 1.69 to suppress immutable field match check when

Rewrite rev. 1.69 to suppress immutable field match check when
extending any table, empty or not:
(cur_obj_is_blank): New.
(fldval_must_match): Use it instead of initialized[].
(getobj): Set it along with cur_obj.
(setstr): Move fldval_must_match() down, so that cur_obj_is_blank is
defined.
(initialized): Remove.