(redraw_overlapping_rows): Use flag overlapping_p.
(direct_output_for_insert): Ditto.
(direct_output_for_insert): Don't use this method if
row is overlapped by others.
(update_text_area): Write full line if current line is overlapped.
(redraw_overlapped_rows): New.
(update_window): Call it.
(redraw_overlapping_rows): New.
(update_window): Call it.
(scrolling_window): Make sure overlapped_p flag in current rows is
unchanged.
(row_equal_p): Take rows overlapped_p flag into account.
(adjust_glyphs): Block input while adjusting matrices.
(direct_output_for_insert): Don't use this
optimization for rows that overlap others.
(update_window_line): Return non-zero if display has changed.
(update_text_area): Ditto.
(update_window): Record if display has been changed.
(blank_row): Compute glyph row's physical height.
(row_equal_p): Take physical row heights into account.
(direct_output_for_insert): Ditto.
(update_text_area): Ditto.