Re: something like linum.el ought to be added

[martin rudalics <rudalics@gmx.at>]

 >>Why do you want to update numbers on any but the selected frame
 >>here?
 >
 >
 > Because I found cases where the previous command created a frame with
 > a buffer that must have its line numbers shown, yet was not selected.

Then you'd have to update line numbers in `after-make-frame-functions'
too.

 >>Also, after scrolling it should be sufficient to consider the
 >>scrolled window only.
 >
 >
 > No: The scrolled window can use overlays that another window needs.

Not if the other window displays another buffer.  For the same buffer
this can be easily handled by giving overlays a window property.

An aside: Sometimes configuration, buffer text, and some window start
position change within one and the same command.  Did you check whether
this cause line number updating run two, three times after the command?