Use const, move declarations to header files.

Use const, move declarations to header files.
* src/buffer.c (Fset_buffer_multibyte): Remove local extern declaration.

* src/character.c (strwidth, parse_str_to_multibyte): Add const.

* src/character.h (strwidth, parse_str_to_multibyte): Likewise.

* src/charset.c (add_to_log): Remove declaration.

* src/composite.c (syms_of_composite): Remove local extern declarations.

* src/data.c (Finteractive_form): Use const.

* src/dired.c (scmp): Add const.
(directory_files_internal): Remove local extern declaration.

* src/dispextern.h (add_to_log): Remove declaration.
(x_get_arg, x_frame_get_arg, x_frame_get_and_record_arg)
(x_frame_get_and_record_arg, x_default_parameter): Add const.

* src/dispnew.c: Remove duplicate #include <unistd.h>.
(update_window, update_frame_1, init_display): Remove local extern
declarations.

* src/editfns.c (region_limit, syms_of_editfns): Remove local extern
declarations.

* src/emacs.c (main): Remove local extern declaration.

* src/font.c (Qnormal, QCtype, QCfamily, QCweight, QCslant, QCwidth)
(QCheight, QCsize, QCname): Remove declarations.

* src/frame.c (x_get_resource_string, x_get_string_resource)
(x_get_arg, x_frame_get_arg, x_frame_get_and_record_arg)
(x_default_parameter): Use const.

* src/image.c (QCwidth, QCheight, QCforeground, QCbackground, QCfile)
(QCdata, QCtype, Qcenter): Remove declarations.

* src/keyboard.h (do_mouse_tracking): Add declaration.

* src/minibuf.c (Qmouse_face): Remove declaration.

* src/msdos.c (IT_note_mouse_highlight): Remove local extern declaration.

* src/xdisp.c (do_mouse_tracking): Remove declaration.
(add_to_log): Use const.

* src/xfaces.c (Qmouse_face): Remove declaration.
(face_color_gray_p, tty_defined_color, defined_color)
(face_color_gray_p, face_color_supported_p). Add const.

* src/xfns.c: Include xlwmenu.h when USE_LUCID.
(x_defined_color, xic_set_xfontset): Use const.
(Fx_hide_tip): Remove local extern declaration.

* src/xselect.c (selection_data_to_lisp_data)
(x_property_data_to_lisp):
* src/xrdb.c (x_get_string_resource, file_p)
(x_get_customization_string, magic_file_p, search_magic_path)
(get_system_app, get_user_app, x_load_resources, x_get_resource)
(x_get_string_resource): Use const.

* src/xterm.c (xlwmenu_window_p, xlwmenu_redisplay): Remove declarations.
(x_text_icon, x_check_errors, x_connection_closed): Use const.

* src/xterm.h (x_get_customization_string, x_load_resources)
(x_get_resource, x_text_icon, x_text_icon, x_check_errors)
(x_check_errors, x_property_data_to_lisp, defined_color)
(xic_set_xfontset, x_defined_color): Use const.