Unify CLI/TUI interface to readline tab completion.

Unify CLI/TUI interface to readline tab completion.

This copies a lot of code from readline, but this is temporary.
Readline currently doesn't export what we need.
The plan is to have something that has been working for awhile,
and then we'll have a complete story to present to the readline
maintainers.

gdb/ChangeLog:

	* cli-out.c: #include completer.h, readline/readline.h.
	(cli_mld_crlf, cli_mld_putch, cli_mld_puts): New functions.
	(cli_mld_flush, cld_mld_erase_entire_line): Ditto.
	(cli_mld_beep, cli_mld_read_key, cli_display_match_list): Ditto.
	* cli-out.h (cli_display_match_list): Declare.
	* completer.c (MB_INVALIDCH, MB_NULLWCH): New macros.
	(ELLIPSIS_LEN): Ditto.
	(gdb_get_y_or_n, gdb_display_match_list_pager): New functions.
	(gdb_path_isdir, gdb_printable_part, gdb_fnwidth): Ditto.
	(gdb_fnprint, gdb_print_filename): Ditto.
	(gdb_complete_get_screenwidth, gdb_display_match_list_1): Ditto.
	(gdb_display_match_list): Ditto.
	* completer.h (mld_crlf_ftype, mld_putch_ftype): New typedefs.
	(mld_puts_ftype, mld_flush_ftype, mld_erase_entire_line_ftype): Ditto.
	(mld_beep_ftype, mld_read_key_ftype): Ditto.
	(match_list_displayer): New struct.
	(gdb_display_match_list): Declare.
	* top.c (init_main): Set rl_completion_display_matches_hook.
	* tui/tui-io.c: #include completer.h.
	(printable_part, PUTX, print_filename, get_y_or_n): Delete.
	(tui_mld_crlf, tui_mld_putch, tui_mld_puts): New functions.
	(tui_mld_flush, tui_mld_erase_entire_line, tui_mld_beep): Ditto.
	(tui_mld_getc, tui_mld_read_key): Ditto.
	(tui_rl_display_match_list): Rewrite.
	(tui_handle_resize_during_io): New arg for_completion.  All callers
	updated.