Omit redundant extern decls.

Omit redundant extern decls.

Most of this patch is from Dmitry Antipov, in:
http://lists.gnu.org/archive/html/emacs-devel/2014-06/msg00263.html
* configure.ac (WERROR_CFLAGS): Add -Wredundant-decls.
* lib-src/emacsclient.c (getenv): Remove decl.
* lib-src/make-docfile.c (write_globals): Add ATTRIBUTE_CONST for
Fbyteorder, Ftool_bar_height, Fmax_char, Fidentity.
* lwlib/lwlib-Xm.c (lw_motif_widget_p, xm_update_one_value)
(xm_create_dialog, xm_destroy_instance, xm_popup_menu)
(xm_set_keyboard_focus, xm_set_main_areas): Remove decls.
* src/commands.h (update_mode_lines):
* src/frame.h (Qbackground_color, Qforeground_color)
(x_set_menu_bar_lines):
* src/ftfont.c (ftfont_font_format):
* src/intervals.h (Qkeymap, Qfont):
* src/keyboard.c (timer_check, safe_run_hooks, Qregion_extract_function):
* src/lisp.h (Ffboundp, Qnil, Qt, Qlambda, Qintegerp, Qwholenump)
(Qsymbolp, Qlisp, Qconsp, Qstringp, Qarrayp, Qbufferp, Qmarkerp)
(Qvectorp, Qbuffer_or_string_p, Qchar_table_p, Qvector_or_char_table_p)
(Qfloatp, Qnumberp, Qfont_spec, Qfont_entity, Qfont_object)
(Fbyteorder, wrong_type_argument, Fmax_char, syms_of_composite)
(Fidentity, extract_float, init_display, syms_of_display, Qdisplay):
(Qimage, Qbox, redisplay_preserve_echo_area, char_table_ref)
(char_table_set, char_table_translate, Qautoload, Qbottom, Qtop)
(Qvisible, Qfont, Qfront_sticky, Qrear_nonsticky, init_sigio)
(Qtool_bar, Qheader_line):
* src/macros.c (Fexecute_kbd_macro):
* src/xdisp.c (Ftool_bar_height, Ftool_bar_height):
* src/xterm.c (x_delete_terminal, XSetIMValues):
* src/xterm.h (x_set_window_size, x_query_color, x_get_focus_frame)
(x_implicitly_set_name, popup_activated)
(widget_store_internal_border):
Remove redundant decls.
* src/frame.c [USE_X_TOOLKIT]: Include widget.h.
* src/keyboard.c (Fexit_recursive_edit, Fabort_recursive_edit):
Remove _Noreturn, as make-docfile now does that for us.
* src/lisp.h (DEFUN): Don't declare fnname here; rely on make-docfile.
(Qregion_extract_function): New decl.
* src/window.c, src/xfns.c: Include menu.h.