All functions rewritten, except when noted above

All functions rewritten, except when noted above
their declaration.  Below is a list of interface changes.
(apply-on-rectangle): New function, mostly replaces
`operate-on-rectangle'.  All callers changed.
(move-to-column-force): Pass new second argument to `move-to-column'.
(kill-rectangle): Added optional prefix arg to fill lines.
(delete-rectangle): Ditto.
(delete-whitespace-rectangle): Ditto.
(delete-extract-rectangle): Ditto.
(open-rectangle): Ditto.
(clear-rectangle): Ditto.
(delete-whitespace-rectangle-line): New function.
(delete-rectangle-line): Added third arg FILL.
(delete-extract-rectangle-line): Ditto.
(open-rectangle-line): Ditto.
(clear-rectangle-line): Ditto.