(comint-highlight-prompt, comint-highlight-prompt-face)

(comint-highlight-prompt, comint-highlight-prompt-face)
(comint-last-prompt-overlay): New variables.
(comint-output-filter): Implement prompt highlighting.
(comint-snapshot-last-prompt): New function.
(comint-send-input): Snapshot the last prompt.
Use comint-highlight-input-face.
(comint-highlight-input-face): Renamed from `comint-highlight-face'.
Use defface instead of defcustom.
(send-invisible, comint-send-eof): Snapshot the last prompt.
(comint-delchar-or-maybe-eof): Use comint-send-eof.
(comint-mode): Make `comint-last-prompt-overlay' buffer-local.