I've merged the line-numbers branch into master. Please report any
problems you see as result of this via 'report-emacs-bug', as usual.
Thanks to everyone who tested the branch and provided feedback.
I noticed that just one of the four variables for this feature has prefix "display-line-number-" instead of "display-line-numbers-".
When all seen together:
it seems like that one 's' got missed in that first variable. Should that variable name be instead "display-line-numbers-width"?