(move-to-column-force): Mark obsolete.

(move-to-column-force): Mark obsolete.
(operate-on-rectangle, delete-extract-rectangle-line)
(insert-rectangle, delete-whitespace-rectangle-line)
(open-rectangle-line, clear-rectangle-line): Use move-to-column.
(string-rectangle-history): New var.
(string-rectangle, string-insert-rectangle): Use it.
(delete-rectangle-line): Fix pos/column mixup and simplify.