* rect.el (operate-on-rectangle): Use move-to-column's FORCE

* rect.el (operate-on-rectangle): Use move-to-column's FORCE
	argument instead of implementing it ourselves.
	(rectangle-coerce-tab): No longer used; deleted.

	* rect.el (open-rectangle): Leave point at the upper corner of the
	rectangle just opened, in imitation of open-line.  Fix doc typo.
	(open-rectangle-line): Use skip-chars-backward's LIM argument to
	leave spaces before the line segment's beginning undisturbed.

	* rect.el: Provide 'rect.