(toplevel): Don't require path-util.

(toplevel): Don't require path-util.
(elmo-spam-bogofilter-program): Don't use `exec-installed-p'.
(elmo-spam-bogofilter-header): Abolish.
(elmo-spam-bogofilter-bogosity-positive-spam-header): Ditto.
(elmo-spam-bogofilter-args): New user option.
(elsp-bogofilter-call-bogofilter): New internal function.
(elmo-spam-buffer-spam-p): Use it.
(elsp-bogofilter-register-buffer): Renamed from
`elmo-spam-bogofilter-register-buffer';
Use `elsp-bogofilter-call-bogofilter'.
(elmo-spam-register-spam-buffer): Follow the change above.
(elmo-spam-register-good-buffer): Ditto.