* xdisp.c: conform to C89 pointer rules

* xdisp.c: conform to C89 pointer rules

(store_mode_line_noprop, display_string, reseat_to_string):
(c_string_pos, number_of_chars, message_dolog):
(message_log_check_duplicate, set_message_1, store_mode_line_noprop):
(display_mode_element, display_string):
Switch between char * and unsigned char * to stay compatible wth
C89 pointer rules.