* indent.el (indent-accumulate-tab-stops): New function.
* textmodes/picture.el (picture-set-tab-stops):
* ruler-mode.el (ruler-mode-mouse-add-tab-stop)
(ruler-mode-ruler): Fix to work with nil tab-stop-list.
* progmodes/asm-mode.el (asm-calculate-indentation): Use
indent-next-tab-stop.