bug#4382: [PATCH] lisp/rect.el: (rectangle-number-lines): New user key binding C-x r N

[Chong Yidong]

> Scott has just informaed me that his FSF assignment papers have been
> processed and cleared. Based on his work at
> http://www.antisleep.com/elisp/gse-number-rect.el I propose following
> new feature to be added to the rect.el package.

I have committed this to the trunk, with some tweaks.  Thanks.