'setopt-local' is the buffer local equivalent of 'setopt'.
Unify 'setopt', 'setopt-local', 'setq-local',
'buffer-local-set-state' with 'setq' to signal
'wrong-number-of-arguments'.
* lisp/cus-edit.el (setopt): Change error signal to
'wrong-number-of-arguments'.
(setopt-local): New macro.
(setopt--set-local): New function.
* lisp/subr.el (set-local): New function.
(setq-local, buffer-local-set-state): Signal
'wrong-number-of-arguments' rather than 'error'.
* doc/emacs/custom.texi (Examining): Document 'setopt-local'.
* etc/NEWS: Announce the new macro and function.
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