New command 'minibuffer-apply'

New command 'minibuffer-apply'

* lisp/minibuffer.el (completions-used-input): New face.
(minibuffer-completion-action): New variable and function.
(minibuffer-completion-command): New variable.
(completing-read-default): Set it to 'this-command'.
(minibuffer-current-input): New function.
(minibuffer-apply): New command.
(minibuffer-local-completion-map): Bind it to 'C-j'.
(minibuffer-local-must-match-map): Unbind 'C-j'.

* lisp/cus-edit.el (customize-toggle-option): Set
'minibuffer-action' property to non-nil.

* etc/NEWS: Announce it.