(redisplay_internal): Clear garbaged frames after

(redisplay_internal): Clear garbaged frames after
resizing mini-window.
(unwind_with_echo_area_buffer): Use
set_buffer_internal_1 instead of set_buffer_internal.
(with_echo_area_buffer): Ditto.
(Vresize_mini_config): New.
(resize_mini_window): Use it to save restore original window
configuration
(syms_of_xdisp): Initialize it.
(reconsider_clip_changes): New.
(redisplay_internal, redisplay_window): Call it.
(mark_window_display_accurate, redisplay_internal): Set current
matrix' buffer, begv, zv.