(handle_single_display_prop): Add parameter

(handle_single_display_prop): Add parameter
DISPLAY_REPLACED_BEFORE_P.  If it is non-zero ignore display
properties which replace the display of text with something else.
(handle_display_prop): Call handle_single_display_prop with
additional argument saying if we already replaced text display
with something else.  Use AREF.
(with_echo_area_buffer_unwind_data, display_menu_bar)
(decode_mode_spec_coding): Use AREF and ASIZE.