(echo_area_display): Use selected frame's minibuf window

(echo_area_display): Use selected frame's minibuf window
but don't set the minibuf_window (don't call choose_minibuffer_frame).
(message2_nolog, message): Likewise.
(echo_area_window): New variable.
(echo_area_display): Set echo_area_window.
(redisplay_window): Distinguish minibuf_window and echo_area_window.

(redisplay): Skip shortcuts if buffer's clip_changed is set.
(redisplay_window): If buffer's clip_changed is set, update mode line.