(ruler-mode-comment-column-char, ruler-mode-goal-column-char)

(ruler-mode-comment-column-char, ruler-mode-goal-column-char)
(ruler-mode-set-goal-column-ding-flag, ruler-mode-mouse-current-grab-object):
New variables.
(ruler-mode-comment-column-face, ruler-mode-goal-column-face): New faces.
(ruler-mode-mouse-set-fill-column): Removed.
(ruler-mode-mouse-grab-any-column, ruler-mode-mouse-drag-any-column-iteration)
(ruler-mode-mouse-drag-any-column): New functions.
(ruler-mode-map): [header-line down-mouse-2] Bound to
`ruler-mode-mouse-grab-any-column' instead of
`ruler-mode-mouse-set-fill-column'.
(ruler-mode): Cleanup buffer local variable `header-line-format' if it didn't
exist when `ruler-mode' was enabled.
(ruler-mode-ruler-help-echo): Updated its value.
(ruler-mode-ruler-help-echo-when-goal-column): New help string used when
goal-column is already set.
(ruler-mode-ruler-help-echo-tab): Renamed to...
(ruler-mode-ruler-help-echo-when-tab-stops): New.
(ruler-mode-fill-column-help-echo, ruler-mode-comment-column-help-echo)
(ruler-mode-goal-column-help-echo): New help strings.
(ruler-mode-ruler): Use `ruler-mode-ruler-help-echo-when-goal-column' instead of
`ruler-mode-ruler-help-echo' if `goal-column' is set. Show `comment-column' and
`goal-column'. Echo the different help string for each *-column characters on
the ruler.