(ruler-mode-left-fringe-cols): New macro.
(ruler-mode-right-fringe-cols): New macro.
(ruler-mode-left-scroll-bar-cols): New macro.
(ruler-mode-right-scroll-bar-cols): New macro.
(ruler-mode-ruler): Use above new macros.
(ruler-mode-left-fringe-cols): Function replaced by more efficient
implementation `ruler-mode-extra-left-cols'.
(ruler-mode-ruler): Use above new function. Take into account
that the fringe areas can now be resized.