Use completion-at-point rather than completion-in-region.

Use completion-at-point rather than completion-in-region.
* lisp/wid-edit.el: Use lexical scoping and move towards completion-at-point.
(widget-complete): Use new :completion-function property.
(widget-completions-at-point): New function.
(default): Use :completion-function instead of :complete.
(widget-default-completions): Rename from widget-default-complete, rewrite.
(widget-string-complete, widget-file-complete, widget-color-complete):
Remove functions.
(file, symbol, function, variable, coding-system, color):
* lisp/international/mule-cmds.el (default-input-method, charset)
(language-info-custom-alist):
* lisp/cus-edit.el (face): Use new property :completions.

* lisp/progmodes/pascal.el (pascal-completions-at-point): New function.
(pascal-mode): Use it.
(pascal-mode-map): Use completion-at-point.
(pascal-toggle-completions): Make obsolete.
(pascal-complete-word, pascal-show-completions):
* lisp/progmodes/octave-mod.el (octave-complete-symbol):
Redefine as obsolete alias.
* lisp/progmodes/octave-inf.el (inferior-octave-completion-at-point):
Signal absence of completion info for old Octave,
(inferior-octave-complete): Redefine as obsolete alias.
* lisp/progmodes/meta-mode.el: Use lexical-binding and completion-at-point.
(meta-completions-at-point): Rename from meta-complete-symbol and
adapt it for use on completion-at-point-functions.
(meta-common-mode): Use it.
(meta-looking-at-backward, meta-match-buffer): Remove.
(meta-complete-symbol): Redefine as obsolete alias.
(meta-common-mode-map): Use completion-at-point.
* lisp/progmodes/make-mode.el: Use lexical-binding and completion-at-point.
(makefile-mode-map): Use completion-at-point.
(makefile-completions-at-point): Rename from makefile-complete and
adapt it for use on completion-at-point-functions.
(makefile-mode): Use it.
(makefile-complete): Redefine as obsolete alias.