(comint-scroll-to-bottom-on-input): Default to nil.

(comint-scroll-to-bottom-on-input): Default to nil.
(comint-mode): Use pre-command-hook, not before-change-function.
(comint-preinput-scroll-to-bottom): Take no arguments.
(comint-output-filter-functions): Renamed from comint-output-filter-hook.
(comint-output-filter): Pass STRING as arg to output hook functions.
(comint-preinput-scroll-to-bottom): Take an arg.
Move point to new process mark if it was at the old one.
Scroll so only if point is at or after the process mark.
When scrolling, put end of text on bottom line, regardless of point.